Mesa 7i76e input current

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09 May 2017 11:04 #92907 by rodw
Hi guys, I've some fairly expensive hardware on its way that has a series of relays that will be used to switch 24v power to 7i76e inputs.

The maximum relay switching current is 50mA and I know the 7i76e can handle much more than that.

Do I need to add current limiting resistors?

If so, what value for the resistor?

Thanks in advance.

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12 May 2017 11:27 #93069 by andypugh
Replied by andypugh on topic Mesa 7i76e input current
I don't think that the 7i76 digital _inputs_ sink any significant current at all.

FIELD INPUT CHARACTERISTICS
The 7I76E field inputs have a nominal input resistance of 10K Ohms to field power
ground. 7I76E inputs sense positive input voltages above a preset threshold. For best
general purpose use, default input threshold is 50% of the field power supply voltage with
10% hysteresis. That is with a 24V field voltage an input must be brought to 60% of 24V
= 14.4V to be sensed as high and then brought to 40% of 24V = 9.6V to be sensed as low.

So at 24V that would be 2.4mA.

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12 May 2017 12:41 #93078 by rodw
Replied by rodw on topic Mesa 7i76e input current
Andy thanks, I thought it would be OK.
I had asked the supplier but there was a bit of a language barrier as this is this cool Pendant turned up from China today and I have not blown it up yet!



They have a number of options and this one has a 5 volt A-B encoder and binary coded scale and axis selection so it should slot into my Mesa 7i76e perfectly. I've got the scale selection switch working but ran out of time tonight. I'll need to do a bit more work in my Hal file to know if everything works as it should.
The receiver has a DIN rail clip and it just becomes a simple wiring exercise to get this going. Well I hope that is the case, but until I know the encoder wheel works, I'll hold my breath!

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