2Wire Prox switch and Micro810

gbradley

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Join Date
Apr 2002
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Corona, Ca.
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On a Micro 810 2080-LC10-12-AWA without a load, the two wire prox won’t light up the Input.
Incidentally on a 24V version Micro 810 2080-LC10-12-QWB without a load, the two wire prox will light up the Input.

On a Micrologix 1400 1766-L32AWAA the 2 wire prox switch works great without a load. No resister needed.

Is there an internal resistor in the Micrologix that allows the prox switch to work without a load?

ProxSetup.PNG
 
The 12AWA Micro 810 is 120VAC inputs.
The 12QWB Micro 810 is 12-24VDC inputs.

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/2080-um001_-en-e.pdf

Edit:
I may have missed something about the switch in question, what voltage or range it is. Or misinterpreted the information given.

Edit2:
Rereading, I realize where my mistake was.

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1766-in001_-en-p.pdf
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/2080-in006_-en-p.pdf

If I'm reading that right, there seems to be a big difference between the impedance of the two AC Inputs. 10kohm on the Micrologix, where as it is 423.7kohm on the Micro 810. So the Micro810 will have much less available off-state current.

I could be interpreting those numbers wrong, but I don't see an off-state leakage current listed on the AC Micro810.
 
Last edited:
TELEMECANIQUE SENSORS
Cylindrical Proximity Sensor, Metal Basic Material, 2 Wire Circuit Type, NO Output Mode
Power Requirement 24 to 240VAC/DC
I just thought that it was curious that it works with the 24VDC Micro 810, but not with the 120VAC Micro810
However Prox switch does work on the Micrologix 120VAC
 
Ya, I realized my mistake when I first posted. I knew how the 2 wire sensors worked, relying on that small leakage current to power the circuitry, but I completely forgot that they come in wide voltage range ac/dc models. I use them very sparingly. From a troubleshooting point of view I've always preferred 3 wire (though I do understand the appeal of 2 wire at times).

It definitely looks like the Micro 810 has a different input circuitry for the AC models than the Micrologix does. And it is pushing the off-state current below the requirement of the switch.
 

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