IO-AI4-AO2 reading problem

[Gabriel Franco]

Hello all.

I just moved an application from V130-33-TA24 to a V1210 using local I/O and remote via EX-RC1, including IO-AI4-AO2.

V130 used one analog input configured as 4-20 mA coming from a weigh scale indicator which has passive analog transmitter. It uses external 12 VDC power supply (Device requires 8-15 VDC as external power supply) different from the 24 VDC used for OPLC. It worked fine for months.

Now, using IO-AI4-AO2 for same purpose and wired the same way, analog input raw value doesn´t move beyond 10.

Tests already performed:

• Doubled checked wiring and configuration.
  
• Analog input using 4-20 mA simulator (Active): works fine.
  
• Current transmitter signal with digital tester: works fine, reading moves up to 12 mA.
  
• Current transmitter signal with digital tester in series with analog module: reading stands about 1.2 mA.
  
• Using another analog input: Same situation, raw value doesn´t change.
  

The only relevant difference I found between analog module and V130 is impedance for analog inputs.

It seems like this particular transmitter is not compatible with IO-AI4-AO2. I have no information about maximum impedance load from transmitter.

Using a resistor in parallel with analog input would be useful?

Any suggestion would be appreciated.

[AlexUT]

Hi,

Please check what is a maximum load impedance for Scale transmitter.

AI4-AO2 have internal impedance 121.5 ohm.

For 130-TA24 it is 37 ohm.

It seems that problem is here.

You can test transmitter with Digital Multimeter and different resistors.

Lets say it works with 100 ohm resistor. Than voltage will be 400-2000 mV.

If 1600 mV range can fit your needs - you can use 0-10V input and linearize it.

If not - you have to look for other transmitter. Or use Current Loop Repeater, if you can find one fitting used Scale transmitter.