Input Min. and Input Max.

ddeshi2

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Hi all, I'm using SCP Add-On Instruction in RSLogix5000. My analog input module is 1756-IF16. My question is what are the Input Min. and Input Max. values for 4-20 ma in ControlLogix.
Is it same as 4ma=3277 and 20ma=16383? or is it different? I couldn't find anywhere in the manual. Please help


Thank you,

Ding
 
Scaling is performed by the 1756-IF16 module. You set up scaling to engineering units when you configure the module. You do not need to scale in your program unless it is necessary to use different scales for the same analog input (for example, display a temperature in both F and C).

In the project tree scroll down to IO Configuration. Double click on the input module. Select the configuration tab. For each input channel first select the channel, then set the correct input range and configure the scaling. The module will return the scaled value to your program. The data type returned by the module is configured when you insert the module, you can choose a REAL or a DINT. To change the data type you have to delete the module from the IO configuration and re-insert it.

A072711-1.jpg
 
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@ Alaric

Thank you for the reply. Actually I want to scale the output and I know Scaling can be done in IO Configuration in ControlLogix. But my case is different, I have one flowmeter and I have to control two valves depending on the output of PID. 4ma-12ma one valve should be opened and 12ma-20ma second valve should be opened while gradually closing the first valve. Attached is the logic that I'm trying to implement using RSLOGIX5000.Is there a method to implement the attached logic without using SCP add-on instruction in RSLOGIX5000?

Thank you,

Ding

MYPROGRAM.jpg MYPROGRAM1.jpg
 

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I have one flowmeter and I have to control two valves depending on the output of PID. 4ma-12ma one valve should be opened and 12ma-20ma second valve should be opened while gradually closing the first valve. Attached is the logic that I'm trying to implement using RSLOGIX5000.Is there a method to implement the attached logic without using SCP add-on instruction in RSLOGIX5000?

Thank you,

Ding

Please explain how gradually first valve is closing while the second one is opening ???
 
Configure your output card in a similar manner as shown above. Configure it to output 4 ma at 0 and 20mA at 100, then configure your PID for 0 to 100% output. Then use a range of 0 to 100 for your logic.

Under ControlLogix you need to think of your analog channels in engineering units. Its a little different than working with SLC hardware, but once you get used to it and forget about doing it the old way, you'll find it to be a lot more flexible and easy to work with.
 
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@widelto

If valve 2 is 10%open then valve 1 should be 10% close, 20%open = 20%close so on

@Alaric
I did as you said ..but I have a question

In the PID Scaling what should I enter for:
Control Variable(CV)
Max (at 100%)=
Min( at 0%)=

Should I enter 0 and 100 or 6242 and 31208 (as 4-20ma)?

Thank you!
 
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0 and 100. Make sure that your output card is configured for Real numbers, not integers.

Forget about 6242 and 31208 - you're still thinking like a SLC.
 
Scaling is performed by the 1756-IF16 module. You set up scaling to engineering units when you configure the module. You do not need to scale in your program unless it is necessary to use different scales for the same analog input (for example, display a temperature in both F and C).

In the project tree scroll down to IO Configuration. Double click on the input module. Select the configuration tab. For each input channel first select the channel, then set the correct input range and configure the scaling. The module will return the scaled value to your program. The data type returned by the module is configured when you insert the module, you can choose a REAL or a DINT. To change the data type you have to delete the module from the IO configuration and re-insert it.

hi alaric and others,

I using a pressure transducer and is currently converting the 4-20ma to 0-100psi reading. Do i key in 0 value for low engineering and 100 for high engineering. I assume it helps to work out to the psi value i want. i do not need to calculate the gradient and offset value?

Do i still need to install a digital pressure gauge just to verify the pressure is accurate?
 
Scaling is performed by the 1756-IF16 module. You set up scaling to engineering units when you configure the module. You do not need to scale in your program unless it is necessary to use different scales for the same analog input (for example, display a temperature in both F and C).

In the project tree scroll down to IO Configuration. Double click on the input module. Select the configuration tab. For each input channel first select the channel, then set the correct input range and configure the scaling. The module will return the scaled value to your program. The data type returned by the module is configured when you insert the module, you can choose a REAL or a DINT. To change the data type you have to delete the module from the IO configuration and re-insert it.

I managed to find out. The low and high enginnering is the desired reading i want. So i should put 0 for low and 100 for high. With respect to the 4ma-20ma. After which, i need to see without pressure. What is the reading. Theortically, it should show o psi. If it show 3 psi. Then it show the transducer is a bit out or offset. In which, i key in 3 to the sensor offset. Am i right? then what is the purpose of doing the calibration?
 
Scaling is performed by the 1756-IF16 module. You set up scaling to engineering units when you configure the module. You do not need to scale in your program unless it is necessary to use different scales for the same analog input (for example, display a temperature in both F and C).

In the project tree scroll down to IO Configuration. Double click on the input module. Select the configuration tab. For each input channel first select the channel, then set the correct input range and configure the scaling. The module will return the scaled value to your program. The data type returned by the module is configured when you insert the module, you can choose a REAL or a DINT. To change the data type you have to delete the module from the IO configuration and re-insert it.

Hi guys,

when i install a transducer of 4-20ma of 0-50psi into the plc.
I had not accurate reading. without applying pressure to it. My plc already show 8ma. And when apply 50psi to it. It show 16ma. What is going wrong?
 
Hi guys,

when i install a transducer of 4-20ma of 0-50psi into the plc.
I had not accurate reading. without applying pressure to it. My plc already show 8ma. And when apply 50psi to it. It show 16ma. What is going wrong?


Put a meter in series with the transducer and verify the above. If it is that
far off then you need to check the calibration or configuration of your transducer.
 
I managed to find out. The low and high enginnering is the desired reading i want. So i should put 0 for low and 100 for high. With respect to the 4ma-20ma. After which, i need to see without pressure. What is the reading. Theortically, it should show o psi. If it show 3 psi. Then it show the transducer is a bit out or offset. In which, i key in 3 to the sensor offset. Am i right? then what is the purpose of doing the calibration?

If you are reading 3 psi when no pressure is applied to the transducer, then the transducer needs calibrating, I would have severe doubts that it was the Analog Input module.

3psi in a 50psi range transducer is a very large error, are we sure this transducer is actually scaled 0-50 psi ?

Is it a new transducer ?
If not, then it could be defective, could it have been damaged, has it been massively over-pressurised at some point in it's working life.

Applying a "Sensor Offset", IMHO, is only a temporary, get-you-going solution. You should either get the transducer bench-tested and calibrated ASAP, or swap it out for a new one.

You mentioned "calibration" - are you referring to the calibration of the analog input module?

You should NEVER perform calibration of an input module using your field devices as the calibration input, but should use precision voltage/current sources. At least one thing in the measurement process has to be relied on.

In my experience, I have never heard of anyone who needed to "re-calibrate" a Logix5000 analog module, but the calibration procedure can be used for certification purposes in regulated industries.
 
Hi guys,

when i install a transducer of 4-20ma of 0-50psi into the plc.
I had not accurate reading. without applying pressure to it. My plc already show 8ma. And when apply 50psi to it. It show 16ma. What is going wrong?

From those figures, I would suggest the transducer is NOT scaled to give

4mA 0psi - 20mA 50 psi
And i have calculated that it is scaled -25 to _75 psi

with those figures quoted, are you still using your AOI, or scaling on the module ??

2011-08-25_232441.jpg
 
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