HC900 PID Disabling

How do I disable a HC900's PID's output using not the PV to the PID, but a second source?

archy said:

How do I disable a HC900's PID's output using not the PV to the PID, but a second source?

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I'm not sure what you are asking exactly. However, if I simply take the first phrase, you can drive the output to 0% output but setting the TRC to a 1 or ON value and setting the TRV to 0.

If you want to drive it to another value while disabled, set the TRV to the value you consider "disabled"

If you are asking to have the PID follow another value, connect a signal tag from the first source to the TRV and set TRC to ON.

Yeah, the way I posted the questions was a bit confusing. But it looks like you answered two of my questions. I will try this. Thank you very much!!!!

I hope you don't mind if I ask another question (BTW: I am brand new to the HC900):

How would I setup an alarm on a temp sensor if its loop output is on and the temp doesn't rise after “X” amount of time.

Are there any textbooks available on the HC900?

archy said:

I hope you don't mind if I ask another question (BTW: I am brand new to the HC900):

How would I setup an alarm on a temp sensor if its loop output is on and the temp doesn't rise after “X” amount of time.

Are there any textbooks available on the HC900?

Click to expand...

The online help files are very good. Contact your local Honeywell Rep for help or you can call the Honeywell Technical Support Center (number in the manuals).

There are several ways to do this, you can use the internal Alarm functionality of the PID. Each of the two alarms have two setpoints. Choose one of the internal alarms and set one setpoint to DEV HI and the other to DEV LOW. If you only care about the temp being LOW, just use one setpoint and make it DEV LOW. Set the amount low that is a problem (say 10ºF) and the alarm will turn on any time the Temperature PV is more than 10ºF below the SP. Connect a timer to the output pin of the PID Block and set it for the amount of time you want to give it to stabilize before alarming.

The second option is the one I prefer. Connect a signal tag to the block that provides the PV (I'll call it TEMP_PV) and then connect a signal tag to the PID block WSP pin (I call that tag TEMP_WSP).

Add an Analog Alarm block and connect TEMP_PV to the PV pin, connect TEMP_WSP to the CV pin, connect a numeric constant to the SP pin and set it to 10 (ºF) to be like the example above then go into the Analog Alarm block and set Use RSP Input, and configure the Hysteresis. Set the Type to Dev Low: (CV-PV) > SP

If your Alarm Delay time is 240 seconds or less, you can use the On Delay setting of the Alarm Block. Otherwise connect a simple timer to it and set the time delay.

The reason I prefer this method is that it is very easy to disable this block using the DISABLE pin when you aren't trying to heat and don't want the alarm.

By the way - Honeywell offers training (for a fee) at least in Fort Washington, PA, but I think they offer it other places.

Thanks again, JHarbin!