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Old February 6th, 2018, 07:49 AM   #1
richleva
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Fancy Exclamation Scale Analogue

Hello,

I'm confused with Instruction called "SCP" with RSlogix. Never really had to use this one, till now.

I need to control an Acid pump at a water treatment plant, Using an analogue output of a PLC. This PLC only has 0-10V analogue output card. So I was going to install a 500Ohm resister to get my 4-20Ma. So at 2Votls will be my 4mA and 10 Volts will be 20mA

If the pump for example is 0-37 liter/hour

I assume the:
Input min is 0
Input Max is 37

How do I figure the Scaled Min and Scaled Max?
Also remembering that 2 Volts should be 4mA

Thanks everyone
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Old February 6th, 2018, 07:56 AM   #2
daba
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What is the model number of the analog output card ?
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Old February 6th, 2018, 07:59 AM   #3
janner_10
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If it were me I would scale the output of the pump to another variable in mA desired. Then use another block to scale the mA to the V.

It will make it easier for the next guy, especially as you can comment the rung, it makes it easy on the eye to what you have done.

So 0 to 37 scales to 4 to 20 then 4 to 20 then scales to say 2000 to 10000, 6554 to 32767 on your OP card (or whatever units it is set for)
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Old February 6th, 2018, 08:30 AM   #4
richleva
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Quote:
Originally Posted by daba View Post
What is the model number of the analog output card ?
Here is the model number of the PLC, There's no cards attached it comes with 2 analogue outputs 0 -10V
1766-L32BXBA
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Old February 6th, 2018, 08:39 AM   #5
richleva
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Quote:
Originally Posted by janner_10 View Post
If it were me I would scale the output of the pump to another variable in mA desired. Then use another block to scale the mA to the V.

It will make it easier for the next guy, especially as you can comment the rung, it makes it easy on the eye to what you have done.

So 0 to 37 scales to 4 to 20 then 4 to 20 then scales to say 2000 to 10000, 6554 to 32767 on your OP card (or whatever units it is set for)
Hi Janner,

What do you mean by (6554 to 32767 on your OP card)?
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Old February 6th, 2018, 10:12 AM   #6
janner_10
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Taken from manual:

Number of inputs 2 single-ended
Voltage output range 010 V DC - 1 LSB
Type of data 12 bit unsigned integer
Step response 2.5 ms @ 95%
Load range Voltage output >1 KΩ
Output coding (010V DC) 04095
Output resolution 12 bit
Analog output setting time 3 ms (max.)
Overall Accuracy
-2060 C (-4140 F) 1.0% of full scale
Electrical isolation Non-isolated with internal logic
Cable length 30 m (98 ft) shielded cable

So your 2v to 10v output would be 819 - 4095.

Something like this:

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Old February 6th, 2018, 10:23 AM   #7
Mickey
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[quote]
Quote:
Originally Posted by richleva View Post
Hello,
I need to control an Acid pump at a water treatment plant, Using an analogue output of a PLC. This PLC only has 0-10V analogue output card. So I was going to install a 500Ohm resister to get my 4-20Ma. So at 2Votls will be my 4mA and 10 Volts will be 20mA

/QUOTE]
Your acid pump is also a load on the circuit. What is it's value?

You are better off using a converter to convert voltage to current.

See link(s) for an example..

https://www.automationdirect.com/adc...er_Input/FC-33

https://www.google.com/search?rlz=1C...w=1671&bih=830
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Last edited by Mickey; February 6th, 2018 at 10:28 AM.
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Old February 6th, 2018, 10:37 AM   #8
Mickey
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Quote:
Originally Posted by janner_10 View Post
Taken from manual:

Number of inputs 2 single-ended
Voltage output range 010 V DC - 1 LSB
Type of data 12 bit unsigned integer
Step response 2.5 ms @ 95%
Load range Voltage output >1 KΩ
Output coding (010V DC) 04095
Output resolution 12 bit
Analog output setting time 3 ms (max.)
Overall Accuracy
-2060 C (-4140 F) 1.0% of full scale
Electrical isolation Non-isolated with internal logic
Cable length 30 m (98 ft) shielded cable

So your 2v to 10v output would be 819 - 4095.

Something like this:

Only one "SCP" is required. First one with scaled min/max at 819-4095.

FYI: the ML1400 will not allow two "SCP"'s on the same rung. It uses RSLogix500 not RSLogix5000.
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Old February 6th, 2018, 11:40 AM   #9
Mickey
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Quote:
Originally Posted by Mickey View Post
Only one "SCP" is required. First one with scaled min/max at 819-4095.

FYI: the ML1400 will not allow two "SCP"'s on the same rung. It uses RSLogix500 not RSLogix5000.

Should have said on the same rung in series, parallel would be ok.
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