Dear All,
what is the exact use of PV paramter in AO block?
Beause in other Vendor's system I could not see this PV parameter in AO block.
Can any one explain with the one example about the application of this parameter?
Thanks,
Manik
It is possible to connect an input signal back to the AO FB. This would typically be a feedback potentiometer providing the true valve position rather than the implied valve position sent to the valve positioner via he output signal
It is often important to indicate the true position of a valve rather than just relying on the value you've sent to the valve.
In the a absence of this feedback signal, IO_READBACK left unconfigured NULL, the PV assumes the value of the output signal. Note the AO can be placed into simulate mode in which case the PV then reflects the simulated value not the output signal.
Be aware, the increase to close option in io_opts changes the sense of the PV value relative to the output value, which can quite often confuse matters. Essentially in traditional 4-20mA an input signal on IO_READBACK of 20mA represents %open. At least this is how I like to imagine it.
In reply to IntuitiveNeil:
Neil ,
Thanks for the input..
Yes I get struct up in the same case...
In the PCSD dynamo for Split range they are using the AO/PV value to show in the dynamo and I am testing in simulation mode.
I was expecting the OUT will show in the dynamo. but it was not.
Could not test PCSD Splitter in Simulation properly.
Thanks.
Mani
In reply to manik:
I discovered the joys of the PCSD dynamos/faceplates and the interpretation of the AO block indications earlier this year. It's not easy to get a consistent interface for operators with the various CSD, CSR and AO module types.
All I know is that AO/OUT value represents the mA value to the field 100%= 20mA always.
When inc to close is enabled, AO/CAS_IN is the invert of AO/OUT.
Intuitively I would always want the %output value shown to the operator to represent the % of maximum of the control signal, whether that be %open for a control valve, %max speed for a VSD, %max heat demand for a heater etc...
I believe PCSD gives this if you have an IO_READBACK signal configured assuming the feedback 100% value represents %maximum control. Unfortunately if you don't have a configured feedback signal it reflects the output signal which in the case of an increase to close valve represents the %minimum (closed) value, which for me isn't intuitively correct.
For additional confusion the PCSD loop faceplates dynamically alters the source parameter used for the output indication based on the SUB_FPDT parameter of the module instance, which has different values for the various controller module types.
I'd suggest that the PCSD faceplates and dynamos in their admirable attempt to be all things to all men have become over complex and confused in their implementation and application.