Analog Input

[2rlp]

Hi,

I have an amplifier which outputs 0 to 5 V depending on the sensed condition. However due to an oversight, I had ordered EX DI16 AI3 TO16 module. This module has 3 Analog inputs of 0 to 20 mA. The amplifier specs state that its output impedance is 100 Ohm, the input impedance of the analog input is 190 Ohms. So on connecting the output of the amplifier to the analog input, I get a value of around 19 mA (978) counts in MI corresponding to the analog input. Is scaling the counts such tha 978 corresponds to 1023, the only solution? Or can the input be made to receive 20 mA?

Thanks

Ron

[Damian]

Ron, Just so that I understand correcly. Is your 0 to 5 volt signal digitial? And you were going to read it with an analog input because of the logic level? But instead you have 0 or 4 to 20mA so you are still trying to read it with the analog input with a direct connection?

[Simon]

Hi Ron,

It looks like you are dealing with an analogue signal, correct?

By my calculations, the best you can expect with a 5V source and 290Ohm total load is 17.2mA. So at 19mA you are getting a better result than you "should" be. You need a load of 250Ohm to get 20mA at 5V. There is no way to do this with the setup you describe.

Either you adjust the span in the PLC with a Linear block, or add a signal conditioner to take the 0...5V input and output it as 4...20mA to suit the PLC

I hope this helps.

[2rlp]

Thank you both Simon & Damian.

The signal is analog. The overrange is set at 5.5V & at this I am getting approximately 19 mA.

Ron

[dahnuguy]

Hi,

I have an amplifier which outputs 0 to 5 V depending on the sensed condition. However due to an oversight, I had ordered EX DI16 AI3 TO16 module. This module has 3 Analog inputs of 0 to 20 mA. The amplifier specs state that its output impedance is 100 Ohm, the input impedance of the analog input is 190 Ohms. So on connecting the output of the amplifier to the analog input, I get a value of around 19 mA (978) counts in MI corresponding to the analog input. Is scaling the counts such tha 978 corresponds to 1023, the only solution? Or can the input be made to receive 20 mA?

Thanks

Ron

What happens when you add a 60 ohm resistor in series with the PLC 190 ohm input?

The 0-5 V out should see 250 ohm.

0-5 V through 250 ohms should give you 0-20 mA.

This assumes that the output device will drive the current.