Hi,
I am new to this industry. I am doing a porject which requires a PLC to process a 4-20mA pressure sensor signal and 4-20mA/PT100 signal from temp. sensor. Can any body tell me, Is there any PLC that accepts Analog input 4-20mA ? please guide me to choose a PLC.

Thanks
[email protected]

 

Probably most of them, if not then it is trivial to adapt 0-10v or 0-20mA inputs.

 

Virtually all of the major ones [PLCs] have analog input and output cards available.

Dave Ferguson
Control Systems Engineer

 

Hello k;
I don't know of any PLC that does not acept 4-20 mA signals. These are industry-standard signals used to link sensors and transmitters to a processing unit (CPU).

The next question is: what do you need to do with these signals once you have read them and scaled them in your PLC? This will become a more important question to help you select your PLC.

Do you need to display the value of these temperature/pressure signals, on an operator screen or on some sort of 7-segment display?
Will you generate alarm signals if they exceed certain values that will control part of a process? Will you need to log and trend these values?

Most low-cost Smart Relays (LOGO! from Siemens, Durus from GE, EASY from Moeller etc...) could handle analog inputs, scale them and control for example pilot lights for alarming.

All brick PLCs (S7-200 by Siemens, Micrologix from Rockwell, and many others) and higher-level PLCs can handle the analog inputs, plus communicate with operator panels/PCs to log, trend, alarm, and do the process control part.

So please define with more accuracy the project you have so we can help you out more precisely.

Hope this helps,
Daniel Chartier

 

Most PLC models have analog I/O capability. You should select one that has the processing capability to do the math you want done on the two signals. If the mathematics is complex, you might do better with a PAC rather than a PLC.

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Hello daniel,

Many thanks for the prompt information. Yes exactly i want. Choose a PLC and i want to do following tasks with the chosen PLC.

My requirements:

1. It should accept 2 Analog inputs.

2. need to display the value of these temperature/pressure signals on a LCD screen, on an operator screen or on some sort of 7-segment display (LCD display Preferable)?

3. generate alarm signals if they exceed certain values that will control part of a process.

4. need to log and trend these values (this is optional)

Could you please suggests PLC models with LCD Display accordingly. Also plz give me your email id.

Many thanks
krishna k
[email protected]

 

Hi Daniel.,

I go through different PLC models and difficult to decide which one to choose..

I am looking for a PLC with 2 analog inputs along with LCD display. To process 2 analog 4-20mA pressure, temperature (PT100) siGnals and Indicate alaram signals if the value exceeds or falls below a specified value.

I am looking for PLC with LCD display to do above task. Also guide me from your perspective becoz i am new to this industry AND willing to learn many things. Your sugestions valuble to me.

If posible mail me at "[email protected]" for quick attention.

Many thanks

 

The tasks you describe

- display analog inputs as digital, numerical values
- generate alarms on the data
- log (save) and trend the data

are what commercially available electronic paperless recorders are designed for, hence they can be configured more far more quickly than a PLC for those who don't already have PLC/HMI programming experience. Recorders are configured, not programmed.

If this is a business project where time is money and not specifically a learning exercise, you will be able to implement a paperless recorder in a fraction of the time it takes you to figure out how to do the same tasks on a PLC/HMI combination.

We use the Honeywell QXZe recorder for projects like you describe.

http://hpsweb.honeywell.com/Cultures/en-US/Products/Instrumentation/paperless/eZtrend/default.htm

Bud

 

That said, you can get several small PLCs with analog inputs and an LCD display. The AB Micrologix line includes at least one, The GE Durus line does also. The Durus is less expensive.

This seems to be a popular category right now and I wouldn't be surprised if the other Majors have something that would meet you needs as well. Try Automation Direct also. This feature set tends to be on very small inexpensive PLCs that are aimed at monitoring and controlling a few points. They have buttons too.

Regards
cww

 

Krishna,

I'm from Indonesia. I think you do not need PLC. All your requirements (except trend) are satisfied with a field based controller. It is cheap, easy and fast to be configured, and lighweight. An example is ABB commander. I even use it for temperatur monitoring.

The price may only in two digits.

However, if there is probability of many additional I/O in the future, you might need PLC.

regards,
Padli