Do-More & pressure transducer used to detect air leak & shut off air supply?

[rayj]

Hi Everyone!

I’m fairly new to programming and using PLC’s.  Recently we installed a new control panel to run our life test system at work.  We build solenoid valves and we cycle our test valves on/off to a set cycle limit to ensure our supplied parts are durable before releasing them for use in production.  We cycle them on 100 psi, sometimes 50 psi as well.  We used a DM CPU with a 9 slot DL-205 rack with 1, D2-16NA input card and 2, D2-08TD2 output cards and various other relays and components.  It has a 10 inch EA9 C-More touch screen which is used to control 9 sets of valve test banks (Up to 90 valves total).  So far I’m really pleased with it and haven’t really had any issues since it was installed at the end of January, 2016.

Occasionally we have a core tube failure where the tube may come apart and create a large air leak.  I am hoping to come up with a cost effective and practical way to have the system automatically cut off the air supply to an individual station if that station has a failure.  I was considering installing one of our valves on each station and using a pressure transducer to detect sizable pressure changes like I would see during a failure.  When the leak is detected the Do-More would then close the supply valve for that individual station. Since I am fairly new to this I was hoping to get some input and ideas for implementing this or something similar.  Any suggestions?  Thank you!

[plcnut]

After you get the transducer connected, then you can use the ALRATE instruction to monitor the transducer.
Here is a copy of the instruction description:

Code: [Select]

  ALRATE - Rate of Change Alarm
 The Rate of Change Alarm instruction (ALRATE) monitors the Input at the specified Sample Time and sets one or both of the designated alarm bit locations if the Input has changed more than the Rate Limit.

 Parameters:
 Input - identifies the memory location to monitor. This can be any readable numeric location.
 Sample Time - specifies the frequency (in milliseconds) at which the comparison between the Input value and the Rate Limit is done. The Sample Time can be any positive integer constant value or any readable numeric location.
 Rate Limit - specifies the maximum allowable change of the Input value from one sample time to the next. The Rate Limit can be any constant value or any readable numeric location.
 Positive Alarm - (if selected) designates the bit location to turn ON if the Input value has increased by more than the Rate Limit since the last Sample Time, otherwise the bit will be turned OFF. This can be any writable bit location.
 Negative Alarm - (if selected) designates the bit location to turn ON if the Input value has decreased by more than the Rate Limit since the last Sample Time, otherwise the bit will be turned OFF. This can be any writable bit location.



[rayj]

Awesome, thank you for the help, PLCNUT!  The ALRATE instruction seems to make sense. 

Do you have a recommendation for the type of transducer output signal to use, such as 4-20 mA or 0-10V DC, etc?  Just wondering what the pros and cons might be of one versus the other. I know they would use different input cards and require different wiring... 

[rayj]

Update:  Actually, after looking around I just found 2, F2-08AD-1 4-20 mA analog input cards on the shelf.  So I will try to just use those I suppose.

[plcnut]

The current cards are more immune to electrical noise than a voltage card. That is the basic difference. I try to use current whenever I can.

[Controls Guy]

Occasionally we have a core tube failure where the tube may come apart and create a large air leak.  I am hoping to come up with a cost effective and practical way to have the system automatically cut off the air supply to an individual station if that station has a failure.  I was considering installing one of our valves on each station and using a pressure transducer to detect sizable pressure changes like I would see during a failure.  When the leak is detected the Do-More would then close the supply valve for that individual station. Since I am fairly new to this I was hoping to get some input and ideas for implementing this or something similar.  Any suggestions?  Thank you!

You could also use either an analog flow transmitter in the same way, or a discrete flow switch with adjustable setpoint, probably thermal dispersion type.  I don't think ADC has those, but ifm, who makes all the ADC pressure and flow instrumentation, does.

I also agree with the recommendation for ma over voltage type transducers for noise immunity. I always use sensors with current output when feasible.