Rif: Re: Measuring AC Line Impedance
I think Don is right: the resistive load measurement is not useful; yo need to measure the e.m.f. and to perform two reactive load measurements in order to solve the equations. - ESAOTE S.p.A. Paolo Peruzzi Research Product DevelopmentDesign Quality Control Via di Caciolle,15tel:+39.055.4229306 I- 50127 Florence fax:+39.055.4223305 e-mail: paolo.peru...@esaote.com I read in !emc-pstc that don_borow...@selinc.com wrote (in of32a3a512.366695dc-on88256c67.00802...@selinc.com) about 'Measuring AC Line Impedance' on Tue, 5 Nov 2002: Part 1. This measurement will NOT give just the resistive part of the source impedance. Your post is so long that it is not clear what you are trying to correct. Also, by top-posting you make it more difficult to understand how your comments relate to previous texts. If we measure the voltage developed across a resistive load, we have one equation with three unknowns, e.m.f., source inductance and source resistance. If we measure the voltage developed across a pure capacitive load (or one with known losses), we also have one equation with three unknowns. If we measure the *open-circuit* voltage, we immediately have the value of one unknown, the e.m.f. or Thevenin equivalent source voltage. That leaves us with two equations and two unknowns, which are soluble. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Measuring AC Line Impedance
John- I was afraid that things were getting long and confusing. The Part 1 and Part 2 comments in my reply refer to the posting immediately below mine. But to answer your fundamental objection. It is indeed true that if we place a resistive and capacitive load, measure voltage amplitude AND phase of the resulting voltage relative to the source (absolute phase), we can then calculate the source resistance and (inductive) reactance of the voltage source. However, if we cannot measure absolute phase of the resulting (loaded) voltage (phase relative to the source voltage), then we are stuck with magnitude-only calculations. Obtaining absolute phase needs some sort of power system clock or stable time reference. Measuring the phase between the current and voltage at the load tells us only about the phase characteristics of the load, and nothing about the voltage source. With the magnitude-only calculations, the resulting voltage equation for a resistive load contains terms in Rs², Xs², and Rs (Rs = source resistance, Xs = source reactance). For pure reactive loads, the resulting voltage equations contain terms in Rs², Xs², and Xs, with the coefficients for Rs² and Xs² in each equation equal. This last property allows one of the two voltage magnitude equations to be scaled such that when the two equations are subtracted from the other, the Rs² and Xs² terms cancel, leaving an equation with Xs as the only unknown. From there, Rs many be found. On the other hand, the voltage magnitude equation for the resistive load does NOT have equal coefficients for the Rs² and Xs² terms. Even if the coefficients were equal, the equation has the Rs term. Remember that the voltage magnitude equiation for the capacitive load contains an Xs term. Scaling and subtrating these two equations would yield an equation with Rs and Xs terms (two unknowns and one equation). Don Borowski Schweitzer Engineering Labs Pullman, WA John Woodgate j...@jmwa.demon.co.uk@majordomo.ieee.org on 11/05/2002 01:23:33 PM Please respond to John Woodgate j...@jmwa.demon.co.uk Sent by:owner-emc-p...@majordomo.ieee.org To:emc-p...@majordomo.ieee.org cc: Subject:Re: Measuring AC Line Impedance I read in !emc-pstc that don_borow...@selinc.com wrote (in of32a3a512.366695dc-on88256c67.00802...@selinc.com) about 'Measuring AC Line Impedance' on Tue, 5 Nov 2002: Part 1. This measurement will NOT give just the resistive part of the source impedance. Your post is so long that it is not clear what you are trying to correct. Also, by top-posting you make it more difficult to understand how your comments relate to previous texts. If we measure the voltage developed across a resistive load, we have one equation with three unknowns, e.m.f., source inductance and source resistance. If we measure the voltage developed across a pure capacitive load (or one with known losses), we also have one equation with three unknowns. If we measure the *open-circuit* voltage, we immediately have the value of one unknown, the e.m.f. or Thevenin equivalent source voltage. That leaves us with two equations and two unknowns, which are soluble. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Measuring AC Line Impedance
I read in !emc-pstc that don_borow...@selinc.com wrote (in of32a3a512.366695dc-on88256c67.00802...@selinc.com) about 'Measuring AC Line Impedance' on Tue, 5 Nov 2002: Part 1. This measurement will NOT give just the resistive part of the source impedance. Your post is so long that it is not clear what you are trying to correct. Also, by top-posting you make it more difficult to understand how your comments relate to previous texts. If we measure the voltage developed across a resistive load, we have one equation with three unknowns, e.m.f., source inductance and source resistance. If we measure the voltage developed across a pure capacitive load (or one with known losses), we also have one equation with three unknowns. If we measure the *open-circuit* voltage, we immediately have the value of one unknown, the e.m.f. or Thevenin equivalent source voltage. That leaves us with two equations and two unknowns, which are soluble. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Measuring AC Line Impedance
Hello, UL emc in Northbrook has the capoability http://www.ul.com/emc/ Regards, Ken Hall -Original Message- From: robert.s...@flextronics.com [mailto:robert.s...@flextronics.com] Sent: Tuesday, November 05, 2002 10:16 AM To: emc-p...@majordomo.ieee.org Subject: RE: Measuring AC Line Impedance Does anyone know of a source of test equipment, purchase or rental, or a test house on the US east coast that can perform the click test described in CISPR 14? Thanks, Robert Seay Flextronics Compliance Labs 762 Park Avenue Youngsville, NC 27596 --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Measuring AC Line Impedance
Does anyone know of a source of test equipment, purchase or rental, or a test house on the US east coast that can perform the click test described in CISPR 14? Thanks, Robert Seay Flextronics Compliance Labs 762 Park Avenue Youngsville, NC 27596 --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Measuring AC Line Impedance
Referring to below... Part 1. This measurement will NOT give just the resistive part of the source impedance. Let Rs = source resistance, Xs = source inductive reactance, and Rl = load resistance, Xc = test capacitor reactance (= 1/2piFC), F = 50 or 60 Hz, and Voc = open circuit voltage. The magnitude of the voltage with a resistive load will be: Vloaded = Voc × magnitude[Rl / (Rs + Rl + jXs)]. Clearly the reactive component will affect the measured voltage when loaded. Part 2. In this case, Vloaded = Voc × magnitude[-jXc/(Rs + jXs - jXc)]. Clearly, the resistive part has an effect on the voltage with a capacitive load. The proposed phase measurement will simply measure the phase shift between the current and voltage in the capacitor, and tells nothing about the phase of the power line voltage source. As I previously stated, since in this measurement the phase of the power line current relative to the open circuit voltage is not available (only voltage magnitudes are available), a capacitor and inductor must be used to make the measurement. Here are the details- Measured voltage with capacitive load (Vc): Vc = Voc × magnitude[-jXc/(Rs + j(Xs - Xc)] =Voc × Xc/sqrt[Rs² + (Xs - Xc)²]. Rearranging: Vc × sqrt[Rs² + (Xs - Xc)²] = Voc × Xc. Squaring both sides, and expanding the (Xs - Xc)² term: Vc² × (Rs² +Xs² - 2XsXc + Xc²) = Voc² × Xc². (Equation #1) Measured voltage Vl with inductive load Xl: Vl = Vc = Voc × magnitude[jXl/(Rs + j(Xs + Xl)] =Voc × Xl/sqrt[Rs² + (Xs + Xl)²]. Rearranging: Vl × sqrt[Rs² + (Xs + Xl)²] = Voc × Xl. Squaring both sides and expanding the (Xs + Xl)² term: Vl² × (Rs² +Xs² + 2XsXl + Xl²) = Voc² × Xl². (Equation #2) Now multiply both sides of Equation #1 by Vl²/Vc²: (Vl²/Vc²) × Vc² × (Rs² +Xs² - 2XsXc + Xc²) =(Vl²/Vc²) × Voc² × Xc² Which is then: Vl² × (Rs² +Xs² - 2XsXc + Xc²) =(Vl²/Vc²) × Voc² × Xc². (Equation #3) Subtracting Equation #3 from Equation #2 yields: Vl² × [2Xs × (Xl +Xc) +Xl² - Xc²] = Voc² × [Xl² - (Vl²/Vc²) × Xc²]. All the values in the above equation are known except for Xs, so Xs can be found. Once the source reactance Xs is known, its value can be substituted into either Equation #1 or Equation #2 and the value of Rs can be determined. Sorry for the long winded answer, and I hope all the math is correct. One more comment: A measurement with a resistive load doesn't help. When compared to Equation #1 or Equation #2, the equivalent equation has terms in Rs², Rs, and Xs. If this equation is scaled and subtracted from Equation #1 or Equation #2, one ends up with a single equation with two unknowns (Rs and Xs) which cannot be solved. Don Borowski Schweitzer Engineering Labs Pullman, WA Spencer, David H david.spen...@usa.xerox.com@majordomo.ieee.org on 10/30/2002 08:57:00 AM Please respond to Spencer, David H david.spen...@usa.xerox.com Sent by:owner-emc-p...@majordomo.ieee.org To:emc-p...@majordomo.ieee.org cc: Subject:RE: Measuring AC Line Impedance Follow up Having just completed an ton of work on this using input I got around here (thanks to Don Borowski, Patrick Lawler, Joe Randolph and John Woodgate). I believe we have characterized the AC mains of our facility. As a sanity check/ technical check can any one comment on process. Part one 1)Open circuit voltage measured. 2)Resistive load placed in circuit. 3) Voltage drop and current measured. 4) Voltage drop divided by current provides resistance component of AC mains. Part 2 1) Open circuit voltage measured. 2)Reactive load placed in circuit (approximately 120uF!) 3) Voltage change (increase really) and current measured (phase angle was recorded to back check math vectorialy). 4) Voltage change divided by current provides reactive component of AC mains. As a side note, I also connected an isolation transformer as the reactive load, the reactive numbers were very very close. The resistive number + reactive number then make up the AC line impedance for this site: Ztest if you will. My two remaining questions: Is this method of characterizing the AC line impedance valid (is there something I'm missing)? Based on my knowledge of these values, and their ratio to the reference impedance(s) specified in EN61000-3-3 and EN61000-3-11, I should be able to calculate and correlate the measured Dmax, Pst, et. al...to the limits specified in those standards. (REFERENCE section 6.1.3 of EN61000-3-11), using our existing AC mains. Any comments or input would be welcome. Thanks Regards David Spencer Xerox Corp. -Original Message- From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Thursday, September 19, 2002 11:56 AM To: emc-p...@majordomo.ieee.org Subject: Re: Measuring AC Line Impedance I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B1D@USAMCMS4) about 'Measuring AC Line Impedance
RE: Measuring AC Line Impedance
I would have expected that the inductance would dominate the branch impedance at line frequency and its harmonics. Ralph McDiarmid, AScT Member Technical Staff Engineering Services Xantrex Technology Inc. www.xantrex.com -Original Message- From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Wednesday, October 30, 2002 11:30 AM To: emc-p...@majordomo.ieee.org Subject: Re: Measuring AC Line Impedance I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B94@USAMCMS4) about 'Measuring AC Line Impedance' on Wed, 30 Oct 2002: Any comments or input would be welcome. It's how I do it. It comes as a surprise to some people that the voltage goes up when you put a big capacitor across the supply. Don't go over the top with BIG caps and resonate the supply inductance. You would NOT like the result, and neither would the electricity supplier. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: measuring AC line impedance (:-)
I did that once. I had been measuring resistance and then needed to measure ac outlet potential, but forgot to change the meter knob position. Now I have a new meter. -- From: Ted Rook t...@crestaudio.com To: emc-p...@ieee.org Subject: measuring AC line impedance (:-) Date: Wed, Oct 30, 2002, 5:42 PM don't you stick the probes in the outlet with the knob set to 'OHMS'? (;o) sorry couldn't resist it. don't try this at home folks. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Measuring AC Line Impedance
David, An interesting test, but of course this only characterizes the line at a single frequency. It might be useful to check line impedance at other frequencies as well, say to the 40th harmonic...? Possibly some modern line analyzers can do this but it seems to me I once had a working setup using a control loop analyzer Bode plotter. But it has been a very long time since I look at such things. Best regards, -doug Douglas E. Powell Compliance Engineer Advanced Energy Industries, Inc. Fort Collins, CO 80535 USA -Original Message- From: Spencer, David H [mailto:david.spen...@usa.xerox.com] Sent: Wednesday, October 30, 2002 9:57 AM To: emc-p...@majordomo.ieee.org Subject: RE: Measuring AC Line Impedance Follow up Having just completed an ton of work on this using input I got around here (thanks to Don Borowski, Patrick Lawler, Joe Randolph and John Woodgate). I believe we have characterized the AC mains of our facility. As a sanity check/ technical check can any one comment on process. Part one 1)Open circuit voltage measured. 2)Resistive load placed in circuit. 3) Voltage drop and current measured. 4) Voltage drop divided by current provides resistance component of AC mains. Part 2 1) Open circuit voltage measured. 2)Reactive load placed in circuit (approximately 120uF!) 3) Voltage change (increase really) and current measured (phase angle was recorded to back check math vectorialy). 4) Voltage change divided by current provides reactive component of AC mains. As a side note, I also connected an isolation transformer as the reactive load, the reactive numbers were very very close. The resistive number + reactive number then make up the AC line impedance for this site: Ztest if you will. My two remaining questions: Is this method of characterizing the AC line impedance valid (is there something I'm missing)? Based on my knowledge of these values, and their ratio to the reference impedance(s) specified in EN61000-3-3 and EN61000-3-11, I should be able to calculate and correlate the measured Dmax, Pst, et. al...to the limits specified in those standards. (REFERENCE section 6.1.3 of EN61000-3-11), using our existing AC mains. Any comments or input would be welcome. Thanks Regards David Spencer Xerox Corp. -Original Message- From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Thursday, September 19, 2002 11:56 AM To: emc-p...@majordomo.ieee.org Subject: Re: Measuring AC Line Impedance I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B1D@USAMCMS4) about 'Measuring AC Line Impedance' on Thu, 19 Sep 2002: Is anyone familiar with a method to measure and calculate those values. The generic values I have for short circuit condition (which include 4 wires in a magnetic conduit) come out higher than my measured values, and those do not include the motor generator source. Put a large capacitor (mains voltage rated) across the mains and measure the voltage change; it may actually increase. You need about 50 uF to get a decent change on 120 V 60 Hz mains. With that result and the one with the resistive load, you can calculate the source impedance as an R and L in series. I'd be interested to learn the result. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http
Re: Measuring AC Line Impedance
I read in !emc-pstc that Robert Macy m...@california.com wrote (in 000801c28045$01fc35c0$b7775142@robertmacy) about 'Measuring AC Line Impedance' on Wed, 30 Oct 2002: Do you have the liberty to share your report - or details and results with the group? The results apply only to that particular outlet at that particular site. But they would still be interesting, even though so far from general. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Measuring AC Line Impedance
I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B94@USAMCMS4) about 'Measuring AC Line Impedance' on Wed, 30 Oct 2002: Any comments or input would be welcome. It's how I do it. It comes as a surprise to some people that the voltage goes up when you put a big capacitor across the supply. Don't go over the top with BIG caps and resonate the supply inductance. You would NOT like the result, and neither would the electricity supplier. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Measuring AC Line Impedance
Do you have the liberty to share your report - or details and results with the group? - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 101 E San Fernando, Suite 402 San Jose, CA 95112 - Original Message - From: Spencer, David H david.spen...@usa.xerox.com To: emc-p...@majordomo.ieee.org Sent: Wednesday, October 30, 2002 8:57 AM Subject: RE: Measuring AC Line Impedance Follow up Having just completed an ton of work on this using input I got around here (thanks to Don Borowski, Patrick Lawler, Joe Randolph and John Woodgate). I believe we have characterized the AC mains of our facility. As a sanity check/ technical check can any one comment on process. Part one 1)Open circuit voltage measured. 2)Resistive load placed in circuit. 3) Voltage drop and current measured. 4) Voltage drop divided by current provides resistance component of AC mains. Part 2 1) Open circuit voltage measured. 2)Reactive load placed in circuit (approximately 120uF!) 3) Voltage change (increase really) and current measured (phase angle was recorded to back check math vectorialy). 4) Voltage change divided by current provides reactive component of AC mains. As a side note, I also connected an isolation transformer as the reactive load, the reactive numbers were very very close. The resistive number + reactive number then make up the AC line impedance for this site: Ztest if you will. My two remaining questions: Is this method of characterizing the AC line impedance valid (is there something I'm missing)? Based on my knowledge of these values, and their ratio to the reference impedance(s) specified in EN61000-3-3 and EN61000-3-11, I should be able to calculate and correlate the measured Dmax, Pst, et. al...to the limits specified in those standards. (REFERENCE section 6.1.3 of EN61000-3-11), using our existing AC mains. Any comments or input would be welcome. Thanks Regards David Spencer Xerox Corp. -Original Message- From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Thursday, September 19, 2002 11:56 AM To: emc-p...@majordomo.ieee.org Subject: Re: Measuring AC Line Impedance I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B1D@USAMCMS4) about 'Measuring AC Line Impedance' on Thu, 19 Sep 2002: Is anyone familiar with a method to measure and calculate those values. The generic values I have for short circuit condition (which include 4 wires in a magnetic conduit) come out higher than my measured values, and those do not include the motor generator source. Put a large capacitor (mains voltage rated) across the mains and measure the voltage change; it may actually increase. You need about 50 uF to get a decent change on 120 V 60 Hz mains. With that result and the one with the resistive load, you can calculate the source impedance as an R and L in series. I'd be interested to learn the result. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Measuring AC Line Impedance
Follow up Having just completed an ton of work on this using input I got around here (thanks to Don Borowski, Patrick Lawler, Joe Randolph and John Woodgate). I believe we have characterized the AC mains of our facility. As a sanity check/ technical check can any one comment on process. Part one 1)Open circuit voltage measured. 2)Resistive load placed in circuit. 3) Voltage drop and current measured. 4) Voltage drop divided by current provides resistance component of AC mains. Part 2 1) Open circuit voltage measured. 2)Reactive load placed in circuit (approximately 120uF!) 3) Voltage change (increase really) and current measured (phase angle was recorded to back check math vectorialy). 4) Voltage change divided by current provides reactive component of AC mains. As a side note, I also connected an isolation transformer as the reactive load, the reactive numbers were very very close. The resistive number + reactive number then make up the AC line impedance for this site: Ztest if you will. My two remaining questions: Is this method of characterizing the AC line impedance valid (is there something I'm missing)? Based on my knowledge of these values, and their ratio to the reference impedance(s) specified in EN61000-3-3 and EN61000-3-11, I should be able to calculate and correlate the measured Dmax, Pst, et. al...to the limits specified in those standards. (REFERENCE section 6.1.3 of EN61000-3-11), using our existing AC mains. Any comments or input would be welcome. Thanks Regards David Spencer Xerox Corp. -Original Message- From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Thursday, September 19, 2002 11:56 AM To: emc-p...@majordomo.ieee.org Subject: Re: Measuring AC Line Impedance I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B1D@USAMCMS4) about 'Measuring AC Line Impedance' on Thu, 19 Sep 2002: Is anyone familiar with a method to measure and calculate those values. The generic values I have for short circuit condition (which include 4 wires in a magnetic conduit) come out higher than my measured values, and those do not include the motor generator source. Put a large capacitor (mains voltage rated) across the mains and measure the voltage change; it may actually increase. You need about 50 uF to get a decent change on 120 V 60 Hz mains. With that result and the one with the resistive load, you can calculate the source impedance as an R and L in series. I'd be interested to learn the result. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Measuring AC Line Impedance
I just ran the math on this. Assuming that you can only measure voltage magnitude (not phase), you need to use a capacitor and an inductor as the loads. Assume that the power source is a voltage with a series resistance R and series reactance jX (where X can be positive or negative). If you do the voltage divider magnitude calculations for each load, you will get equations in R², X², X, and a constant. In each equation, the coefficient of R² and X² will be the same. One equation can be multiplied by a constant to make the coefficients for R² and X² the same in both equation. When the equations are subtracted, the difference is an equation in X and a constant, so the value of X is found. This value of X can be substituted back into either equation to solve for R. If a resistor is used as a load, the voltage divider magnitude calculation yields an equation in R², X², R, and a constant. It is not possible to combine this with one of the other voltage divider magnitude equations and come up with an equation with a single unknown variable. Don Borowski Schweitzer Engineering Labs Pullman, WA John Woodgate j...@jmwa.demon.co.uk on 09/19/2002 08:55:53 AM Please respond to John Woodgate j...@jmwa.demon.co.uk To: emc-p...@majordomo.ieee.org cc:(bcc: Don Borowski/SEL) Subject: Re: Measuring AC Line Impedance I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B1D@USAMCMS4) about 'Measuring AC Line Impedance' on Thu, 19 Sep 2002: Is anyone familiar with a method to measure and calculate those values. The generic values I have for short circuit condition (which include 4 wires in a magnetic conduit) come out higher than my measured values, and those do not include the motor generator source. Put a large capacitor (mains voltage rated) across the mains and measure the voltage change; it may actually increase. You need about 50 uF to get a decent change on 120 V 60 Hz mains. With that result and the one with the resistive load, you can calculate the source impedance as an R and L in series. I'd be interested to learn the result. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list This e-mail may contain SEL confidential information. The opinions expressed are not necessarily those of SEL. Any unauthorized disclosure, distribution or other use is prohibited. If you received this e-mail in error, please notify the sender, permanently delete it, and destroy any printout. Thank you.
Re: Measuring AC Line Impedance
I just ran the math on this. Assuming that you can only measure voltage magnitude (not phase), you need to use a capacitor and an inductor as the loads. Assume that the power source is a voltage with a series resistance R and series reactance jX (where X can be positive or negative). If you do the voltage divider magnitude calculations for each load, you will get equations in R², X², X, and a constant. In each equation, the coefficient of R² and X² will be the same. One equation can be multiplied by a constant to make the coefficients for R² and X² the same in both equation. When the equations are subtracted, the difference is an equation in X and a constant, so the value of X is found. This value of X can be substituted back into either equation to solve for R. If a resistor is used as a load, the voltage divider magnitude calculation yields an equation in R², X², R, and a constant. It is not possible to combine this with one of the other voltage divider magnitude equations and come up with an equation with a single unknown variable. Don Borowski Schweitzer Engineering Labs Pullman, WA John Woodgate j...@jmwa.demon.co.uk on 09/19/2002 08:55:53 AM Please respond to John Woodgate j...@jmwa.demon.co.uk To: emc-p...@majordomo.ieee.org cc:(bcc: Don Borowski/SEL) Subject: Re: Measuring AC Line Impedance I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B1D@USAMCMS4) about 'Measuring AC Line Impedance' on Thu, 19 Sep 2002: Is anyone familiar with a method to measure and calculate those values. The generic values I have for short circuit condition (which include 4 wires in a magnetic conduit) come out higher than my measured values, and those do not include the motor generator source. Put a large capacitor (mains voltage rated) across the mains and measure the voltage change; it may actually increase. You need about 50 uF to get a decent change on 120 V 60 Hz mains. With that result and the one with the resistive load, you can calculate the source impedance as an R and L in series. I'd be interested to learn the result. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list This e-mail may contain SEL confidential information. The opinions expressed are not necessarily those of SEL. Any unauthorized disclosure, distribution or other use is prohibited. If you received this e-mail in error, please notify the sender, permanently delete it, and destroy any printout. Thank you.
Re: Measuring AC Line Impedance
Hi Dave: I had the same question some time back, and came up with the following process. 1) For the resistive component, I applied a resistive load to the AC line, and calculated R = dV/dI 2) For the inductive component, I measured the transient current through an 'X' capacitor at the moment it was touched across the AC line. This requires a storage scope, and a current sense resistor or current probe. Amplitude accuracy is not important, since you're concerned with the period of the ringing. There is a big spike of current, followed by several cycles of ringing. I calculated the line inductance from the ringing frequency. For those who want more precision: - If you know the resonant frequency of the 'X' capacitor assembly, you can calculate the stray inductance, and adjust the line inductance accordingly. - Once you calculate the line inductance, you can correct the steady state impedance in step 1. Patrick Lawler plaw...@west.net On Thu, 19 Sep 2002 08:06:18 -0400, Spencer, David H david.spen...@usa.xerox.com wrote: I'm trying to characterize the 50Hz AC line impedance of my facility, for comparison to the values specified in IEC61000-3-3. I've come across generic short circuit values for the Resistive and Inductive components. However, I need to determine exactly what these values are ideally through a combination of measurement and calculation. So far, I've taken a large resistive load and measured the voltage drop on the AC line. From that I calculated the total impedance of the AC line. However, as you may suspect, with a resistive load, the power factor is 1.0. So I can't vectorly, calculate the resistive and inductive components. Is anyone familiar with a method to measure and calculate those values. The generic values I have for short circuit condition (which include 4 wires in a magnetic conduit) come out higher than my measured values, and those do not include the motor generator source. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Measuring AC Line Impedance
In a message dated 9/19/2002, you write: So far, I've taken a large resistive load and measured the voltage drop on the AC line. From that I calculated the total impedance of the AC line. However, as you may suspect, with a resistive load, the power factor is 1.0. So I can't vectorly, calculate the resistive and inductive components. Hi Dave: I am not familiar with the specific measurement you are trying to make, so the following may not be applicable to your situation. However, some of the basic concepts may be useful. In the telecom business it is sometimes necessary to know the complex impedance presented by a 2-wire port. In theory, if you drive the port with a voltage source applied through a known resistance, you can calculate the complex impedance of the port based on measurements of the following two things: 1) The voltage drop across the source resistor 2) The phase of the current through the resistor, relative to the phase of the source I designed a simple fixture to measure the voltage and phase, then derived the necessary equations and created a spreadsheet to calculate the complex impedance. Soon after completing my measurements this way, I got a good price on a used test instrument that makes this measurement directly. I was very pleased to find that the values measured by the test instrument matched my calculated values almost exactly. This gave me good confidence in my earlier test method, even though I no longer need to use it. It might be possible for you to adapt this method for the test you want to make. If so, I would be happy to send you a copy of the equations and a copy of the spreadsheet I used. Since this was developed internally for my own use, the notes are a little sketchy, but I think I could fill in the gaps with a telephone conversation. While I am not familiar with the details of the test you are trying to perform, I can see that one possible complication would occur if the test is supposed to be performed under a specified load condition. In that case, you would have to find a way to ensure that the AC impedance of your load does not affect the measured impedance of the mains. I think there are ways to accomplish this either with a test fixture or by making the spreadsheet calculations take the load impedance into account. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com HTMLFONT FACE=arial,helveticaFONT SIZE=2In a message dated 9/19/2002, you write:BR BR BR BLOCKQUOTE TYPE=CITE style=BORDER-LEFT: #ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5pxSo far,nbsp; I've taken a large resistive load and measured the voltage drop onBR the AC line.nbsp; From that I calculated the total impedance of the AC line.BR However, as you may suspect, with a resistive load, the power factor is 1.0.BR So I can't vectorly, calculate the resistive and inductive components.nbsp; BR /BLOCKQUOTEBR BR BR Hi Dave:BR BR I am not familiar with the specific measurement you are trying to make, so the following may not be applicable to your situation.nbsp; However, some of the basic concepts may be useful.BR BR In the telecom business it is sometimes necessary to know the complex impedance presented by a 2-wire port.nbsp; In theory, if you drive the port with a voltage source applied through a known resistance, you can calculate the complex impedance of the port based on measurements of the following two things:BR BR 1) The voltage drop across the source resistorBR 2) The phase of the current through the resistor, relative to the phase of the sourceBR BR I designed a simple fixture to measure the voltage and phase, then derived the necessary equations and created a spreadsheet to calculate the complex impedance.BR BR Soon after completing my measurements this way, I got a good price on a used test instrument that makes this measurement directly.nbsp; I was very pleased to find that the values measured by the test instrument matched my calculated values almost exactly.nbsp; This gave me good confidence in my earlier test method, even though I no longer need to use it.BR BR It might be possible for you to adapt this method for the test you want to make.nbsp; If so, I would be happy to send you a copy of the equations and a copy of the spreadsheet I used.nbsp; Since this was developed internally for my own use, the notes are a little sketchy, but I think I could fill in the gaps with a telephone conversation.BR BR While I am not familiar with the details of the test you are trying to perform, I can see that one possible complication would occur if the test is supposed to be performed under a specified load condition.nbsp; In that case, you would have to find a way to ensure that the AC impedance of your load does not affect the measured impedance of the mains.nbsp; I think there are ways to accomplish this either with a test fixture or by
Re: Measuring AC Line Impedance
I read in !emc-pstc that Spencer, David H david.spen...@usa.xerox.com wrote (in 052106A55179D611B34300096BB02E3F8B1D@USAMCMS4) about 'Measuring AC Line Impedance' on Thu, 19 Sep 2002: Is anyone familiar with a method to measure and calculate those values. The generic values I have for short circuit condition (which include 4 wires in a magnetic conduit) come out higher than my measured values, and those do not include the motor generator source. Put a large capacitor (mains voltage rated) across the mains and measure the voltage change; it may actually increase. You need about 50 uF to get a decent change on 120 V 60 Hz mains. With that result and the one with the resistive load, you can calculate the source impedance as an R and L in series. I'd be interested to learn the result. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Measuring AC Line Impedance
In a message dated 9/19/2002, you write: So far, I've taken a large resistive load and measured the voltage drop on the AC line. From that I calculated the total impedance of the AC line. However, as you may suspect, with a resistive load, the power factor is 1.0. So I can't vectorly, calculate the resistive and inductive components. Hi Dave: I am not familiar with the specific measurement you are trying to make, so the following may not be applicable to your situation. However, some of the basic concepts may be useful. In the telecom business it is sometimes necessary to know the complex impedance presented by a 2-wire port. In theory, if you drive the port with a voltage source applied through a known resistance, you can calculate the complex impedance of the port based on measurements of the following two things: 1) The voltage drop across the source resistor 2) The phase of the current through the resistor, relative to the phase of the source I designed a simple fixture to measure the voltage and phase, then derived the necessary equations and created a spreadsheet to calculate the complex impedance. Soon after completing my measurements this way, I got a good price on a used test instrument that makes this measurement directly. I was very pleased to find that the values measured by the test instrument matched my calculated values almost exactly. This gave me good confidence in my earlier test method, even though I no longer need to use it. It might be possible for you to adapt this method for the test you want to make. If so, I would be happy to send you a copy of the equations and a copy of the spreadsheet I used. Since this was developed internally for my own use, the notes are a little sketchy, but I think I could fill in the gaps with a telephone conversation. While I am not familiar with the details of the test you are trying to perform, I can see that one possible complication would occur if the test is supposed to be performed under a specified load condition. In that case, you would have to find a way to ensure that the AC impedance of your load does not affect the measured impedance of the mains. I think there are ways to accomplish this either with a test fixture or by making the spreadsheet calculations take the load impedance into account. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
re: Measuring AC
I want to thank everyone for the great information I got in response to my question about measuring AC. One thing I hadn't thought about with my off-the-cuff idea of simply using a voltage divider is the issue of isolating the AC return and the circuit board return. Not isolating these raises a variety of issues that I'm not prepared to deal with. So, I think they need to be isolated. The method suggested by Jonathan Malton strikes me as a really elegant and highly accurate solution to the problem. This involves the use of a voltage controlled oscillator and an optoisolator. Using op-amps for rectifying diodes is also a great idea I think. The problem of providing a separate off-line power supply for the VCO, sort of takes some of the fun out of the idea, but this problem is, nevertheless manageable. I'm also going to review IEC950 and IEC1010 as suggested by Horst Haug. The basic problem with transformers is that it's not possible to get a specification on their accuracy. In talking to Signal Transformer, they give me a verbal specification of +/-2% accuracy (no load). Advanced Components Industries, OTH, provide a verbal specification of +/-10%. The difference might be in the size of the transformers. The Signal transformer is relatively large and relatively expensive. The Advanced Transformer is of the PCB type and is very small (0.6 inches high). The lady at Advanced seems to be very knowledgeable and says that the accuracy is not simply a function of turns ratio, but also depends on the wire and core construction. She claims that they can calculate transformer accuracy simply by looking at the wire and core specifications. Max mkel...@es.com
RE: Measuring AC
Max Your idea should work. On the old PS300/390 we did a similar thing to extract a 50/60hz clock signal. A VDE opto-isolator is critical to this design however. -- From: Max[SMTP:mkel...@chekov.corp.es.com] Sent: Thursday, January 16, 1997 9:21 AM To:emc-p...@ieee.org Subject: Measuring AC Does anyone know of a good method (or have any ideas) of how I could reduce line voltage down to low (DC) levels in order to measure the line voltage with an AD converter. Using a transformer is obviously the easiest way and probably provides the least potential problems with safety agencies. But transformers are not (I don't think) terribly accurate and they are rather bulky even in this sort of application. What are the safety implications, for example, of just rectifying and filtering the voltage and running it through a voltage divider? Thanks, Max Kelson mkel...@es.com
Re: Measuring AC
Hi Max YouAsked Does anyone know of a good method (or have any ideas) of how I could reduce line voltage down to low (DC) levels in order to measure the line voltage with an AD converter. Why not just use a precision voltage divider, and then feed the reduced ac voltage to your A/D. If you need only positve voltage, then couple into the A/D with a capacitor and add a precise DC offset voltage. Using a transformer is obviously the easiest way and probably provides the least potential problems with safety agencies. But transformers are not (I don't think) terribly accurate and they are rather bulky even in this sort of application. Probably not the best way to do it! What are the safety implications, for example, of just rectifying and filtering the voltage and running it through a voltage divider? I am not a safety engineer however, I wouldn't think this is any less safe than using this same method for normal dc voltage supply! Many TV receivers use this basic idea for their supplies! But this method for your requirement is more costly than above. Regards Tony O'Hara Sales Engineer Technical Marketing Co
Re: Re: Measuring AC
Hello, You might use clause 2.4 of IEC950 or clause or clause 6.3.1.2 of IEC1010 depending what standard is valid for your equipment. LIMITED CURRENT CIRCIUT. In this way you should be able to avoid the use of transformer or optocoupler. This enables you to measure on AC (primary) and connect to the measurement circuit. Please read also 2.2.8.2 IEC950 as a guideline, how you could bridge reinforced isolation Primary to SELV by resistors !! regards Horst * Dipl.-Ing. (FH) Horst Haug INTERTest Systems GmbH ProduktsicherheitSudetenstr. 5 Product-Safety D - 87600 Kaufbeuren Tel. : +49 8341/91-5051 FAX : +49 8341/91-5059 E-Mail: ho...@it-kf.mhs.compuserve.com WWW : http://ourworld.compuserve.com/homepages/intertest_germany *
