more Mesa 7i77 and Proximity Switches

Hello All,

Right now, I have four Honeywell 922AA1Y-A4N-L inductive proximity switches. ( part of the original machine ) Like these - LINK HERE

Reading here, it seems that these are not _as_ suitable for use as similar PNP types ( what that means to me, I have no idea ) when using a 7i77. But, knowing that, and desiring to keep my build finish as simple as possible, what would others that have 'been here, done this" recommend for purchasing to use in place of these? I've tried searching, but didn't really see any specific references or recommendations.

If there is something better, by all means, feel free to point me in that direction, too.

A year later, I'm finally finding the time to button this thing up ( I hope ). Have only had the bits and pieces laying around forever....

Thanks.

The 7I77 inputs expect an external positive voltage to be applied to the inputs

NPN type sensors will not work directly with 7I77 inputs because
their outputs only sink current (to ground) but do not source current.

NPN sensors can be made work if you add a pullup resistor per input:

+24V --> resistor pin1
resistor pin2 --> PROX_OUT and 7I77 input

suggested resistor value is 2K 1W

PNP type sensors will work directly connected to 7I77 inputs

Peter, thanks for the reply. Questions below.

PCW wrote:

The 7I77 inputs expect an external positive voltage to be applied to the inputs
NPN type sensors will not work directly with 7I77 inputs because
their outputs only sink current (to ground) but do not source current.

Okay. Now I understand a little better. So there's a "golden rule"... Thanks. I do not quite "get" the next though...

PCW wrote:

NPN sensors can be made work if you add a pullup resistor per input:

+24V --> resistor pin1
resistor pin2 --> PROX_OUT and 7I77 input

This is where it gets fuzzy for me again...
So if I'm understanding you correctly, it looks a little like this -
24V+ --> 2Kohm/1Watt resistor --> Proximity sensor OUTPUT wire AND these both go into the 7i77 input terminal.
This leaves two wires on the Prox Sensor... one of which is presumably the GND wire...

What's the third wire for/do/go to?

PCW wrote:

suggested resistor value is 2K 1W

PNP type sensors will work directly connected to 7I77 inputs

Thank you for that.
Would these be a better ( or even acceptable ) choice? PROX SENSOR LINK HERE

What PCW wrote was only regarding the output signal wire and you got it correctly.
Of course you must then also connect supply voltage to the sensor.

For proximity sensors it is usually brown cable for + supply, blue cable for 0v supply (ground) and black wire for the signal.

The new sensor you linked is a pnp sensor and then you don't need the pull up resistor. Just connect the black wire (if you have a standard colored M12 sensor connection cable) to 7i77 input, blue to 0v and brown to 24v.

bobobo,


Thank you for taking the time. I appreciate it. That helps.
An EE friend stopped by just now and also explained the prox sensors to me, as well. His napkin doodle helps immensely.

After listening to you guys, I think I may try to use these sensors and do the inverting trick. Already got some resistors this morning.

Thank you very much.

Okay. So I'm a little confused. I'm hoping it is the equipment, but willing to accept that it's the nut behind the probe.

So, I wired a sensor up, thusly -

24VDC Switching Power Supply ( DIN rail mounted )
Connected 120VAC to the input side.
Connected the Brown wire of the sensor to the Positive side of the 24VDC side.
Connected the Blue wire of the sensor to the Negative side of the 24VDC side.
Connected the 2Kohm/1W resistor to the Black wire of the sensor.
Connected the other end of the resistor to the same Positive side of the 24VDC side.

Initially, I got nothing.

Then, after thinking a bit, I ran a wire from the GND of the 24VDC side, to the DIN rail.

Then, I put the Negative probe from the VOM on the DIN rail and the Positive probe to the Black wire of the sensor. ( with resistor )

With sensor untriggered, I read nothing. ( nothing to .4 VAC )
With the sensor triggered, I read 7.9 - 8.0 VAC.

Now, I'm hoping two things here -
I'm hoping that the AC readings are just my crappy little DMM not being able to switch between AC and DC automagically at lower voltages. ( they actually have a rep for that... ) And, that this 8.0 Volts is good enough for the 7i77 to work with. Otherwise, do I just change the resistor's value ( different resistor ) to something lesser to allow more voltage through?

Otherwise, that's a neat trick! Thanks for explaining it to me, Peter and bobobo.

If the output does not swing close to 24V something is wrong
I would verify your resistor and your voltmeter (try it on the 24V)

Yep. You are correct, Sir.

Fiddled around with it a bit and thought to try another sensor.
That one works as expected. So, one of my sensors is buggered.
Ironically, this might have been the starting point for how I came to own this thing...

Thank you. Again.