RE: Open-loop detection on analog output cards
We do exactly that. We have a few FBM 4.s where we take the output and feed it back to an AIN block then use an alarm block (differential alarm). Seems to work very well. Dennis Sloan Arizona Public Service -Original Message- From: Loyd Greer [mailto:[EMAIL PROTECTED]] Sent: Tuesday, May 15, 2001 5:39 PM To: Foxboro DCS Mail List Subject: Re: Open-loop detection on analog output cards Would it be possible to loop the 4-20 ma output through a 4-20 ma input and alarm it in the ain block? Another way might be to add a low value resistor in the loop and monitor a voltage drop across it with an FBM 02.This would take an extra input for each loop. I do not know what type of isolation problem, if any, you might run into. I would wire it to a different FBM. If this would work it would save you from having to install a position transmitter on the valve. Loyd Greer Original Message - From: Rick Rys [EMAIL PROTECTED] To: Foxboro DCS Mail List [EMAIL PROTECTED] Sent: Thursday, May 10, 2001 6:52 PM Subject: RE: Open-loop detection on analog output cards Let's assume you have an FBM 04 with ECB type 2, and a simple AIN, PID(A), AOUT analog control loop. Next you remove the wiring at the FBM terminal for the 4-20ma output for this channel. The CP is good, the fieldbus is good, and the FBM is good. ECB Failsafe is not enabled. The field wiring is bad (open), however, and the valve is getting 0ma and thus going to it's failure state. You will likely be getting some alarms soon enough, but I understand why you might want to get an alarm immediately. This might be possible with intelligent transmitters, but it is my understanding that the FBM04 is not smart enough to identify a single open loop output. Inputs would be caught by out of range, but I don't think there is any way to detect a bad output short of a valve position transmitter with some type of deviation alarming scheme. In the AOUT block the BAO when set to 1 has alarming looking at BAD (BO193AX Block Book). BAD is set from the OPSTAT of the ECB block (with some logic I could not find), but the ECB is only setting the BAD based on communication related errors (see ECB Block description) and not disconnected output wires. You can look at BAD, OPSTAT, or ECBSTA to verify that nothing is showing as bad. Maybe someone else could verify this behavior as I didn't check it on real hardware. Rick Rys R2 Controls --- This list is neither sponsored nor endorsed by the Foxboro Company. All postings from this list are the work of list subscribers and no warranty is made or implied as to the accuracy of any information disseminated through this medium. By subscribing to this list you agree to hold the list sponsor(s) blameless for any and all mishaps which might occur due to your application of information received from this mailing list. To be removed from this list, send mail to [EMAIL PROTECTED] with unsubscribe foxboro in the Subject. Or, send any mail to [EMAIL PROTECTED] --- This list is neither sponsored nor endorsed by the Foxboro Company. All postings from this list are the work of list subscribers and no warranty is made or implied as to the accuracy of any information disseminated through this medium. By subscribing to this list you agree to hold the list sponsor(s) blameless for any and all mishaps which might occur due to your application of information received from this mailing list. To be removed from this list, send mail to [EMAIL PROTECTED] with unsubscribe foxboro in the Subject. Or, send any mail to [EMAIL PROTECTED] --- This list is neither sponsored nor endorsed by the Foxboro Company. All postings from this list are the work of list subscribers and no warranty is made or implied as to the accuracy of any information disseminated through this medium. By subscribing to this list you agree to hold the list sponsor(s) blameless for any and all mishaps which might occur due to your application of information received from this mailing list. To be removed from this list, send mail to [EMAIL PROTECTED] with unsubscribe foxboro in the Subject. Or, send any mail to [EMAIL PROTECTED]
Re: Open-loop detection on analog output cards
Yes, but it would be much cleaner if it were just part of the AO FBM's onboard diagnostics. I would even settle for a single A/D for all output channels, multiplexed between them on a 5 or 10 second cycle, if circuitry or PC board space is an issue. Thanks to all who responded. Corey Clingo Sr. Engineer BASF Corporation Would it be possible to loop the 4-20 ma output through a 4-20 ma input and alarm it in the ain block? Another way might be to add a low value resistor in the loop and monitor a voltage drop across it with an FBM 02.This would take an extra input for each loop. I do not know what type of isolation problem, if any, you might run into. I would wire it to a different FBM. If this would work it would save you from having to install a position transmitter on the valve. Loyd Greer --- This list is neither sponsored nor endorsed by the Foxboro Company. All postings from this list are the work of list subscribers and no warranty is made or implied as to the accuracy of any information disseminated through this medium. By subscribing to this list you agree to hold the list sponsor(s) blameless for any and all mishaps which might occur due to your application of information received from this mailing list. To be removed from this list, send mail to [EMAIL PROTECTED] with unsubscribe foxboro in the Subject. Or, send any mail to [EMAIL PROTECTED]
Re: Open-loop detection on analog output cards
To answer Kevin Fitzgerrell's question, I am opening the loop at the FBM. Neither the detail display nor system management shows anything awry. The output is therefore not initialized and can be manipulated. My experience agrees with what Rick Rys said. I was hoping that the FBM could be coerced into reading back its loop output current and comparing it with what was being asked for by the FBM, and alarm if these were different. The other system I have experience with (Honeywell) does this and generates an alarm and initializes upstream blocks if the commanded output current and the actual loop current do not agree. It is a handy troubleshooting tool and I miss it :-( Corey Clingo Sr. Engineer BASF Corp. --- This list is neither sponsored nor endorsed by the Foxboro Company. All postings from this list are the work of list subscribers and no warranty is made or implied as to the accuracy of any information disseminated through this medium. By subscribing to this list you agree to hold the list sponsor(s) blameless for any and all mishaps which might occur due to your application of information received from this mailing list. To be removed from this list, send mail to [EMAIL PROTECTED] with unsubscribe foxboro in the Subject. Or, send any mail to [EMAIL PROTECTED]
Re: Open-loop detection on analog output cards
How/where are you opening the loop? Have you checked the block's detail display to see if you are getting any indication there? Regards, Kevin FitzGerrell --- Corey R Clingo [EMAIL PROTECTED] wrote: Pardon me for being ignorant, but how does one implement open-loop detection on analog outputs? I have tried setting BAO to 1, but opening the loop still does not generate an alarm. TIA, Corey Clingo Sr. Engineer BASF Corporation _ http://messenger.yahoo.com.au - Yahoo! Messenger - Voice chat, mail alerts, stock quotes and favourite news and lots more! --- This list is neither sponsored nor endorsed by the Foxboro Company. All postings from this list are the work of list subscribers and no warranty is made or implied as to the accuracy of any information disseminated through this medium. By subscribing to this list you agree to hold the list sponsor(s) blameless for any and all mishaps which might occur due to your application of information received from this mailing list. To be removed from this list, send mail to [EMAIL PROTECTED] with unsubscribe foxboro in the Subject. Or, send any mail to [EMAIL PROTECTED]
RE: Open-loop detection on analog output cards
Let's assume you have an FBM 04 with ECB type 2, and a simple AIN, PID(A), AOUT analog control loop. Next you remove the wiring at the FBM terminal for the 4-20ma output for this channel. The CP is good, the fieldbus is good, and the FBM is good. ECB Failsafe is not enabled. The field wiring is bad (open), however, and the valve is getting 0ma and thus going to it's failure state. You will likely be getting some alarms soon enough, but I understand why you might want to get an alarm immediately. This might be possible with intelligent transmitters, but it is my understanding that the FBM04 is not smart enough to identify a single open loop output. Inputs would be caught by out of range, but I don't think there is any way to detect a bad output short of a valve position transmitter with some type of deviation alarming scheme. In the AOUT block the BAO when set to 1 has alarming looking at BAD (BO193AX Block Book). BAD is set from the OPSTAT of the ECB block (with some logic I could not find), but the ECB is only setting the BAD based on communication related errors (see ECB Block description) and not disconnected output wires. You can look at BAD, OPSTAT, or ECBSTA to verify that nothing is showing as bad. Maybe someone else could verify this behavior as I didn't check it on real hardware. Rick Rys R2 Controls --- This list is neither sponsored nor endorsed by the Foxboro Company. All postings from this list are the work of list subscribers and no warranty is made or implied as to the accuracy of any information disseminated through this medium. By subscribing to this list you agree to hold the list sponsor(s) blameless for any and all mishaps which might occur due to your application of information received from this mailing list. To be removed from this list, send mail to [EMAIL PROTECTED] with unsubscribe foxboro in the Subject. Or, send any mail to [EMAIL PROTECTED]
