Structured Text Pump Control - PLCS.net

WuShockKS · April 7th, 2021, 01:53 AM

Hello,
I am new to plcs and using structured text IEC 61131-3.

I want to turn off and on a pump based on level setpoints from an analog signal. I have the text.

if tankLevel > HighSP then
hspump1out := 0.0;
elsif tanklevel < LowSP then
hspump1out := 1.0;
end_if;

But how do I get the program to repeat? Once the level lowers to kick on the pump the program ends and does not turn off at the top setpoint.

Thanks

L D[AR2,P#0.0] · April 7th, 2021, 02:10 AM

Post a screen shot of your code running with the level greater than the setpoint. Also post how your floating point hspump1out controls the pump off/on

WuShockKS · April 7th, 2021, 02:22 AM

I didn't understand floating point HS1Pumpout. It is a single digital output bit.

parky · April 7th, 2021, 02:47 AM

Never seen that normally it should be true or false as outputs for pumps etc. will be digital (Boolean) not floats.
The code would normally be called cyclically in a task so runs every scan.

cardosocea · April 7th, 2021, 02:51 AM

Silly question, but what platform is this? This reminds me of the OMRON (20 odd years ago) that needed an instruction to tell them to cycle the program at the end of the program. Perhaps your platform has similar?

drbitboy · April 7th, 2021, 05:49 AM

Is it ELSIF or ELSEIF in this implementation? help.codesys.com seems to use ELSIF, but there are a few occurrences of ELSEIF there.

L D[AR2,P#0.0] · April 7th, 2021, 07:17 AM

Here is an example showing the value of the variables when the plc is running. Your screen shot does not show any, it is a repeat of your original post in a different format.

Mara · April 7th, 2021, 07:43 AM

Pump is turned ON if the value is higher than HighSp and OFF if value is lower than LowSp. My question is: what if the value is BETWEEN the low- and high limit?

Edit: You will need something like this (don't know exactly since i don't know your application)

IF Level < LowSp AND level <HighSp THEN

Pump:=TRUE;

ELSE

Pump:= FALSE;

END_IF

drbitboy · April 7th, 2021, 07:50 AM

Quote:

Originally Posted by Mara

Pump is turned ON if the value is higher than HighSp and OFF if value is lower than LowSp. My question is: what if the value is BETWEEN the low- and high limit?

No change from the previous scan's value; this is bang-bang control with a hysteresis gap.

ndzied1 · April 7th, 2021, 07:55 AM

Quote:

Originally Posted by WuShockKS

But how do I get the program to repeat? Once the level lowers to kick on the pump the program ends and does not turn off at the top setpoint.

Thanks

The program (POU in IEC speak) should be in a “task” that repeats.

Tom8940 · April 7th, 2021, 04:59 PM

Alternating pump control.jpg
Perhaps this can help you on the way

April 7th, 2021, 01:53 AM	#1
WuShockKS Member Join Date: Mar 2021 Location: Kansas Posts: 3	Structured Text Pump Control Hello, I am new to plcs and using structured text IEC 61131-3. I want to turn off and on a pump based on level setpoints from an analog signal. I have the text. if tankLevel > HighSP then hspump1out := 0.0; elsif tanklevel < LowSP then hspump1out := 1.0; end_if; But how do I get the program to repeat? Once the level lowers to kick on the pump the program ends and does not turn off at the top setpoint. Thanks

April 7th, 2021, 02:10 AM	#2
L D[AR2,P#0.0] Lifetime Supporting Member Join Date: Nov 2006 Location: UK Posts: 6,227	Post a screen shot of your code running with the level greater than the setpoint. Also post how your floating point hspump1out controls the pump off/on __________________ S7-300 to 1500 conversions done - email to s7conversions@hotmail.com

April 7th, 2021, 07:43 AM	#8
Mara Member Join Date: Jan 2017 Location: Finland Posts: 83	Pump is turned ON if the value is higher than HighSp and OFF if value is lower than LowSp. My question is: what if the value is BETWEEN the low- and high limit? Edit: You will need something like this (don't know exactly since i don't know your application) IF Level < LowSp AND level <HighSp THEN Pump:=TRUE; ELSE Pump:= FALSE; END_IF Last edited by Mara; April 7th, 2021 at 07:51 AM.

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April 7th, 2021, 02:47 AM	#4
parky Member Join Date: Oct 2004 Location: Midlands Posts: 3,097	Never seen that normally it should be true or false as outputs for pumps etc. will be digital (Boolean) not floats. The code would normally be called cyclically in a task so runs every scan.

April 7th, 2021, 02:51 AM	#5
cardosocea Member Join Date: Nov 2016 Location: Fields of corn Posts: 1,815	Silly question, but what platform is this? This reminds me of the OMRON (20 odd years ago) that needed an instruction to tell them to cycle the program at the end of the program. Perhaps your platform has similar?

April 7th, 2021, 05:49 AM	#6
drbitboy Lifetime Supporting Member Join Date: Dec 2019 Location: Rochester, NY Posts: 2,602	Is it ELSIF or ELSEIF in this implementation? help.codesys.com seems to use ELSIF, but there are a few occurrences of ELSEIF there.

April 7th, 2021, 04:59 PM	#11
Tom8940 Member Join Date: Jun 2018 Location: Denamrk Posts: 4	Alternating pump control.jpg Perhaps this can help you on the way

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