reat0ng

1756-hsc/b problem

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i'm converting from plc-5 to 1756-L71,old one uses 1771-VHSC to calculate how much water been added.

the old program set the counter to Counter Mode,No Store,Rollover = 0,Preset = 0 and Scaler = 0. wiring on Input A

and i do all the same on rslogix 5000 with 1756-HSC,but the data has a little deviation at about 10% compare to original data

how to solve this problem? thanks

https://imgur.com/ywWV99n

https://imgur.com/0npVCxJ

https://imgur.com/VSpTPFS

https://imgur.com/2fVKOcW

https://imgur.com/olP0CR8

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Thanks for the screenshots !

Those appear to show that your PLC-5 code used a data block starting at N9:84 that was 44 Words long to configure the 1771-VHSC.    The screenshots of N84 show that all the values in that data block are zero, which suggests that the VHSC was configured for all defaults, which you've assessed to mean Counter Mode, No Store, Rollover = 0, Preset = 0, and Scaler  = 0.

What kind of pulse signal does your flowmeter generate ?   What's the voltage, what's the pulse rate, and how long (in ms) are the pulses ?   I'd have to look up the default filters on the 1771 and 1756 modules to see if they're similar.

How do you evaluate your flow;   do you count up a number of seconds then capture the Accumulated Count, then calculate the flow ?

Could the logic that triggers that calculation be different between the two systems ?

Is the ControlLogix sending this flowmeter data back to the PLC-5 for you to do that calculation (I see that there's some copying of the 32-bit value into ControlLogix tags that are equivalent to N8:70-71 and N8:72-73)  ?

Is the deviation of the volume flow consistently above the old measurements, or consistently below, or is it always different ?

 

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10 hours ago, Ken Roach said:

thanks for replying! 

since the case is just a PLC updating work,i don't know what signal such as pulse rate and the period sent from the flowmeter.

i'll check the voltage tomorrow,maybe it just the voltage input causes the deviation.

and because the ladder wasn't written by me so i don't quite know the whole program,but the data won't back to PLC-5 since there is no more wired and powered off.

the deviation of the volume PLC is always higher than the meter display in control room,very strange.

 

 

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Does the control room meter display get its signal from the same flowmeter output ?

When you change over a PLC to a new model, most of the I/O and signals work in a similar way.   But they aren't always exactly the same, so you need to research signals like this one.

I don't think it's fair to say "it's very strange" until you have examined the whole system and program.

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4 hours ago, Ken Roach said:

Does the control room meter display get its signal from the same flowmeter output ?

When you change over a PLC to a new model, most of the I/O and signals work in a similar way.   But they aren't always exactly the same, so you need to research signals like this one.

I don't think it's fair to say "it's very strange" until you have examined the whole system and program.

the meter display in the control room is used for setting water flow volume,and show how much water has been added in the machine.

and it sends signal to PLC  to show on FTView SE.

i'll check it out what kind of signal the meter display sends.

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