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]
