Analog

rashmorbius said:

I am using an Allen-Bradley MicroLogix 1200 along with an AB 1762-IF4 4 channel analog input card. I need to hook up an analog level probe using 4-20ma. The probe uses three wires; one of the wires is positive, another negative and the third is the wiper (like using a potentiometer).

First, I am looking for a good 4-20 isolator. I am currently using a Weidmuller WAS5 PRO RTD which has the potentiometer setup, but it is not reliable.

Second, I am using a SCP (scale with parameters) to record the anlog input, but that hasn't been too successufl either.

Can anyone shed some light on this

Click to expand...

John Soltesz said:

What do you need the isolator for? If the level probe is only connected to the PLC it shouldn't matter. I believe you have a 3 wire sensor. One sensor wire goes to the +24VDC power supply and the other goes to the 24vdc common. The third sensor wire would go to the + input of whatever channel you are using and the - input would go to the 24vdc common. Check your documentation. I am not familure with this module but check if there are any dip switches or jumpers to set it for 4-20ma input. You may need to configure the module channel for 4-20ma also. Check your documentation.

The SCP should be the same as an SLC500, I haven't done any ML1200's. You need to setup the count input with it referencing the analog input register used. I am not sure if it is 31206 for 20ma and 6241 for 4ma. Something like that, check your documentation. The engineering units would be the range of the sensor or you could use 0-100% if you are not sure. How is the level sensor setup? Measuring depth with 4ma at tank empty? Probably. Check your documentation. The SCP would put the result in whatever register you desire to record. Would you be using integer or floating point?

Click to expand...

rashmorbius said:

You are right, I went through the manual (again) and actually figured out what AB was trying to specify (not always a small feat with AB) with their wiring diagram for the 1762-IF4 module.

Also, I will be using an integer to record, do you think floating point would be better?

Click to expand...