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V350-J-RA22 Analog Inputs failing


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I have a job using a V350-J-RA22 and use one of the analog inputs from a 2 wire sensor, the sensor has a 24v wire powering it and then a wire to the PLC sending 4-20mA.

However a recurring issue is happening which we cannot fault find the reason why, where the analog inputs are blowing/ stop working.

Our only thought is to do with the datasheet as highlighted where it says max input rating 1.1V, and were sending into the PLC around 6V or so.

So if this is the issue how do I go about stopping this from happening in future/ why is it not seeming to be an issue when I've done a similar program with sensor on a unistream.

And if this is not the issue, what could be causing the analog inputs to stop working from the 2 wire sensor we have?

Screenshot 2022-09-06 090637.png

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  • MVP 2023

What you have encountered is a constant problem in PLCs with current input.

When connecting the sensor, the user can accidentally short-circuit the 4-20mA line with the +24V power line. It can also be during the operation of the sensor - for example, someone cut the cable. The consequences are like yours. For a load of 37 Ω +24 V creates an overcurrent of 0.6 A. This is a complete annihilation of the analog input.

Standard question - what to do?

I have two solutions for such cases:

1. An expensive solution is to use an external galvanically decoupled analog signal to analog 4-20mA to 4-20mA or 4-20mA to 0-10V converter.

2. A cheap solution is to buy a high-precision 500Ω resistor and connect it between the 0V ground and the analog input turned on in the 0-10V mode. We read values in the range of 2-10V - which corresponds to the range of 4-20mA for the sensor you need. In the event of a short circuit, you will see smoke from the resistor if its power is less than 2W. Usually, the analog input in the 0-10V mode from +24V does not suffer.

I also encountered 220VAC applied to the analog input - the consequences are even more terrible - the PLC usually breaks if the analog inputs are not isolated. And even if they are insulated - there is a lot of smoke!!!

Another case is when the wires to the analog inputs pass close to the frequency converter... The problems are also significant - sometimes it ends fatally.

 

P.S. Most recently, I had a case with a new module EX-D16A3-TO16 where user destroyed three current inputs in a row - because I said that in case of problems with one, there are two more spare and I made a software switch for redundancy - it did not help. :(

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12 minutes ago, kratmel said:

What you have encountered is a constant problem in PLCs with current input.

When connecting the sensor, the user can accidentally short-circuit the 4-20mA line with the +24V power line. It can also be during the operation of the sensor - for example, someone cut the cable. The consequences are like yours. For a load of 37 Ω +24 V creates an overcurrent of 0.6 A. This is a complete annihilation of the analog input.

Standard question - what to do?

I have two solutions for such cases:

1. An expensive solution is to use an external galvanically decoupled analog signal to analog 4-20mA to 4-20mA or 4-20mA to 0-10V converter.

2. A cheap solution is to buy a high-precision 500Ω resistor and connect it between the 0V ground and the analog input turned on in the 0-10V mode. We read values in the range of 2-10V - which corresponds to the range of 4-20mA for the sensor you need. In the event of a short circuit, you will see smoke from the resistor if its power is less than 2W. Usually, the analog input in the 0-10V mode from +24V does not suffer.

I also encountered 220VAC applied to the analog input - the consequences are even more terrible - the PLC usually breaks if the analog inputs are not isolated. And even if they are insulated - there is a lot of smoke!!!

Another case is when the wires to the analog inputs pass close to the frequency converter... The problems are also significant - sometimes it ends fatally.

 

P.S. Most recently, I had a case with a new module EX-D16A3-TO16 where user destroyed three current inputs in a row - because I said that in case of problems with one, there are two more spare and I made a software switch for redundancy - it did not help. :(

Thanks for the reply, we also tried this solution of a software switch to be able to utilise both inputs, however we have now gone through about 3 V350s with all the Analog inputs not working, we have bought a 

S1SL-1AI-1C

Signal conditioner

we have tested it wired up with a signal generator to the PLC but not yet to the complete system with the actual 2 wire sensor, but am unsure yet to if this is the right product/ will work?

 We have wired the PLC for the customer so I doubt the issue is them shorting the 4-20mA line with +24V, and for it to happen now to 5 analog inputs is baffling, so we shall try the signal conditioner we bought and see if that resolves the issue, if not, we will have to try your other solution!

Thanks again

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  • 4 weeks later...

I have also problems with the analog inputs of a V350-35-R34. At first I took a PT1000 probe with 4-20 mA converter with 2-wire-connection. Nothing happend and I thought it was about a too low voltage to drive the converter. So then I used a adjustable signal generator with externel power supply. That generater works proper fine without  the PLC. With the PLC  there are running only 3.2 to 3.5 mA. What is my problem? Perhaps sombody can help me.

Thanks in advance

 
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On 10/2/2022 at 5:49 AM, der_bruchpilot said:

I have also problems with the analog inputs of a V350-35-R34. At first I took a PT1000 probe with 4-20 mA converter with 2-wire-connection. Nothing happend and I thought it was about a too low voltage to drive the converter. So then I used a adjustable signal generator with externel power supply. That generater works proper fine without  the PLC. With the PLC  there are running only 3.2 to 3.5 mA. What is my problem? Perhaps sombody can help me.

Thanks in advance

 

Are you sure that have the correct settings on the dip switches on the PLC? at least on the ones that I use there is  a setting in the software but you need to also change a dipswitch inside the PLC.

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On 10/9/2022 at 11:04 AM, der_bruchpilot said:

Those who can read have a clear advantage.

That was the problem. I only saw the software-parameters and diddn't realize, that there olso some hardware jumpers.

Thank you very much.

like a former colleague used to say, "I'm not an expert, I just read the manuals" (though, He actually was the expert in that company he was the product manager of PLCs)

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  • MVP 2023
8 minutes ago, Fernando Castro said:

like a former colleague used to say, "I'm not an expert, I just read the manuals"

And nowadays most tech experts just know how to use Google. Seems like every day I get a question from a friend or family and all I do is type their exact question into Google and give them the answer I find there.

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