PLC-5 to L81E PID Conversion

So I think I can run a MSG to read those tags every 200ms, 20ms might be a challenge

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If you have the budget and a reason to use it, the 1756-RIO module has a "ghost mode" that allows it to listen to RIO I/O and Block Transfers without affecting the scantime or addressing of a RIO network.

This isn't the original multipurpose 1756-DHRIO; the 1756-RIO is an A-B Remote I/O scanning engine based on hardware and firmware built by QTS in Florida. Its network-based cousin the "AN-X" is distributed and supported through ProSoft, and has similar features available.

Mispeld said:

With independent gains, and the new loop update time specified correctly, I would actually multiply integral gain, Ki, by 10.

This is my thinking: in the PLC-5 the loop was being told update time was 0.2 seconds. So when it was integrating (summing) error it was multiplying error by that 200 ms interval before adding it. But, you were actually doing this 10 times faster at the 20 ms scan rate. This is basically equivalent to a 10x increase in integral gain. After correcting the loop update time setting you will need to move this "artificial" 10x factor into the gain itself, to get the same response. This is regardless of the actual update time (within reason), so long as it is correctly specified in the PID block.

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That makes sense...Thank you!

Ken Roach said:

If you have the budget and a reason to use it, the 1756-RIO module has a "ghost mode" that allows it to listen to RIO I/O and Block Transfers without affecting the scantime or addressing of a RIO network.

This isn't the original multipurpose 1756-DHRIO; the 1756-RIO is an A-B Remote I/O scanning engine based on hardware and firmware built by QTS in Florida. Its network-based cousin the "AN-X" is distributed and supported through ProSoft, and has similar features available.

Click to expand...

You know I believe that the customer has some ProSoft AN-X modules. A previous integrator tried to upgrade the Panelview 1200 to a Panelview Plus using them to bridge to the DH+ network. He did such a horrible job on the conversion, moved everything around, renamed stuff, stuck a bunch of brightly colored trends on it...the operators hated it and it was terrible responding to operator entries so they hired us to re-do it with a G15. I just used a serial cable to the PLC-5 for my HMI and started with the 1980s graphics from the Panelview1200 which the operators like better any way.

To make a short story long, they still have that module in the panel and connected and two other boilers have them installed in the panels (but not connected), so I am pretty sure I can borrow one.

With all that said, I don't think it would let me listen to the backplane block transfer going from the analog card to its CPU, but perhaps I could spy on the transfers going between the analog rack and the digital one which include those same values.

I setup a quick simulation, Loop1 PID instruction (independent) is running in a 200ms periodic task, loop update time is set for 0.2s, Kp=0,1,Igain=0.1, Loop2 is identical except running is a 20ms task. Screen2 is the same step change in set point the other direction, but with the Igain of loop1 set to 1 (10x)