The LTC6102 is even better (did not notice it before) with 10uV max offset. That lets you use a very small series resistor (in the milli-ohm range) and still have milliamp resolution and several amps of full scale dynamic range.
I am in the process of doing exactly what you are talking about (power supply remote monitoring and control). I currently have a Maxim current sense chip in my power supply (MAX471, no longer manufactured) which I will replace with probably the LT6102, the processor is a TI MSC1210 which, for all its quirks, has a 24 bit A/D converter built in. The voltage reference is an AD580, not the best but sufficient and I have several of those. I have used that chip before to plot the current draw versus temperature of an HP 10811's oven. The temperature was measured using a 10k NTC thermistor and the A/D converter of the same TI chip: http://www.ko4bb.com/Test_Equipment/HP10811-Current.png Here is the link to the Linear Tech page on high side current sense (again): http://www.linear.com/ad/current_sense.jsp Didier KO4BB > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Didier Juges > Sent: Friday, January 18, 2008 5:26 AM > To: 'Discussion of precise time and frequency measurement' > Subject: Re: [time-nuts] Slightly OT: inexpensive USB > analog-digitalconverter? > > Be careful that if you do not isolate the A/D converter > analog circuits from the USB ground, you may create all sorts > of nasty ground loops with the computer. When dealing with > power supplies, it's always best to be isolated. > I do not know enough about USB to know if it can be simply > isolated with opto couplers, but I know that RS-232 is very > easy to isolate. So if your data rate is not great, a serial > solution would be easier to implement (even if you go through > a serial-USB adapter for convenience on the PC side) > > Linear Technology, Analog Devices and Maxim have hot side > current sense chips that are accurate and cheap. They are > specialized diff amps, not regular IA. LT for instance has > one that has less than 50uV offset (LT1787, see Design Note 227) > > Didier KO4BB > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Hal Murray > > Sent: Friday, January 18, 2008 3:55 AM > > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] Slightly OT: inexpensive USB > analog-digital > > converter? > > > > > > > (My goal is to add digital voltage and current monitoring to some > > > older bench power supplies.) > > > > Measuring voltage is simple. If the input range is too > big, you need > > a few resistors. If it's small, you lose a few bits from > the top of > > the A/D. Add an op-amp if you need them. > > > > Measuring current gets tricky. > > > > There are several chips designed for measuring current on > 48V busses. > > I think they are just an instrumentation amplifier with big enough > > resistors on the front end so that the common range goes up to 48V. > > > > Alternatively, if the supply is floating, you can put the sense > > resistor in the ground lead, but you still need a good amplifier to > > make the signal big enough for an ADC. > > > > > > -- > > These are my opinions, not necessarily my employer's. I hate spam. > > > > > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > No virus found in this incoming message. > > Checked by AVG Free Edition. > > Version: 7.5.516 / Virus Database: 269.19.2/1223 - Release > > Date: 1/13/2008 8:23 PM > > > > > > No virus found in this outgoing message. > Checked by AVG Free Edition. > Version: 7.5.516 / Virus Database: 269.19.2/1223 - Release > Date: 1/13/2008 > 8:23 PM > > > > _______________________________________________ > time-nuts mailing list -- [email protected] To unsubscribe, > go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.516 / Virus Database: 269.19.2/1223 - Release > Date: 1/13/2008 8:23 PM > > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.19.2/1223 - Release Date: 1/13/2008 8:23 PM _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
