0-20 mV and 4-20 mA analog inputs, which PLC?

[thecarb]

Hi all,

I have a project, where I need 2 x 4-20 mA (2-wire) pressure transmitter and 1 oxygen transducer with 0-20 mV output.

In the past, I tried to use that oygen transducer with Vision V570 and V200-18-E3XB snap-in I/O. We have succesfully read the input with that configuration. However, last week I tried to connect that oxygen transducer to a Jazz JZ20-T18 alongside with 2 x 4-20 mA pressure transmitter and we couldn't get the measurement from that oxygen transducer.  I don't know what the problem really is but I thought that the resolution or the un-isolated inputs can be the problem(s). Jazz has 10 bit, un-isolated inputs and Vision has 14 bit isolated ones.

Which PLC model should I use? We need touch-screen display and a model with a lower price would be better, of course if it is possible.

 

Thanks in advance.

[Flex727]

4 hours ago, thecarb said:

...and 1 oxygen transducer with 0-20 mV output.

Do you mean 0-20 mA or 0-10 V?

[Joesteva]

The resolution shouldn't be a problem, did you configure the input to be 0-10V? the resolution will only affect your measurement by making it more or less precise depending on the case. Try measuring the output of the Oxygen transducer, since its 0-10V you can just put the probes on the Analog Module.

[AlexUT]

Hi,

SB95 is the system bit to change the resolution of the analog input (for Jazz 2 only).
It enables 12-bit analog input sampling (0-4095).
Turn it ON at power-up. It is OFF by default (10-bit, 0 to 1023)
If you don’t see it in the comments, please try restore System Symbols - Menu -> Restore SB default symbols.

[Simon]

As above, the resolution will not prevent you from getting a reading.  You mention 2-wire transducers.  Firstly just work with the Oxygen transducer, as I assume it is a 3 or 4 wire device?  I would expect the Jazz to read it fine.  If you are including the 2-wire devices in the IO wiring they may be interfering with the readings.

Also when you say you "couldn't get the measurement" what does that mean exactly?  Was the value 0, 1024, 32767?  Did it vary at all when the oxygen level varied, even if it was the incorrect value?

With the 2-wire devices, the Unitronics PLCs do not provide loop power for 2-wire analogue transmitters.  You will need a power supply for loop power and the best way to do this is to use an isolation module with loop power capability.

[thecarb]

On 5/25/2017 at 4:28 PM, Flex727 said:

Do you mean 0-20 mA or 0-10 V?

I mean 0 - 20 mili V.

 

On 5/25/2017 at 5:49 PM, Joesteva said:

The resolution shouldn't be a problem, did you configure the input to be 0-10V? the resolution will only affect your measurement by making it more or less precise depending on the case. Try measuring the output of the Oxygen transducer, since its 0-10V you can just put the probes on the Analog Module.

Yes I configured the input as 0-10 V.

 

7 hours ago, Simon said:

As above, the resolution will not prevent you from getting a reading.  You mention 2-wire transducers.  Firstly just work with the Oxygen transducer, as I assume it is a 3 or 4 wire device?  I would expect the Jazz to read it fine.  If you are including the 2-wire devices in the IO wiring they may be interfering with the readings.

Also when you say you "couldn't get the measurement" what does that mean exactly?  Was the value 0, 1024, 32767?  Did it vary at all when the oxygen level varied, even if it was the incorrect value?

With the 2-wire devices, the Unitronics PLCs do not provide loop power for 2-wire analogue transmitters.  You will need a power supply for loop power and the best way to do this is to use an isolation module with loop power capability.

Oxygen transducer has 2 wires, so you don't need to feed this, it gives 0-20 mV output according to O2 composition. As we have sold that sytem with Jazz PLC, I don't have the chance to try it. The value was "0" when I connect oxygen transducer with other 4-20 mA pressure transmitters.

[Flex727]

5 hours ago, thecarb said:

I mean 0 - 20 mili V.

I'd be very surprised if you can get anything meaningful on a 0-10V analog input from a 0-20mV sensor, especially if it is a 10-bit resolution input.

[Ausman]

The key words here are "0-20mV transducer".  It will work fine if you run it through a conditioner that will give you a usable output.  A quick google brings up many examples.

As Flex says, 0-20mV will not give you much resolution, if you get it to read at all.  But couple it to a conditioner and it will.  14 bit vs 10 bit may have given you a reading, but it wouldn't have been very useable, unless you're simply looking to see if O2 is there or not.

cheers,

Aus