Wiring questions for 7i96 plasma (WILL OUTPUT BE REVERSED?)

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08 Sep 2021 06:00 #219910 by Ekholm
Hi! When using NPN sensors i will connect power supply-positive To 7i96 ground.How will output for my relay work? Will output be reversed?Why i ask is that i will use a relay to trigger the plasma switch, and need a flyback diode to handle the voltage spike.Or do you think i can remove the relay and connect it directly?

I have attached a picture for how i think i should do the wiring. All the sensors is already bought so i´m stuck with PNP sensors for the home switches, one trigger swich for floating z.
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14 Sep 2021 17:37 #220632 by andypugh

Hi! When using NPN sensors i will connect power supply-positive To 7i96 ground.
 

My first thought is that this sounds like a terrible idea....

Tie all the grounds together. Power the NPN sensor from field power in the usual way. 
Tie the NPN sensor output to the field power + at the 7i96 with a 1k resistor. 
Think of an NPN sensor as a switch connected to GND. With the switch open the resistor pulls the input to +FV. With the switch closed the sensor pulls it down to (very close to) GND. 
 
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14 Sep 2021 20:21 - 14 Sep 2021 20:25 #220646 by PCW
Yes, the inputs should work as-is
(if the input common is at +24V, the input will sense
connection to ground so will work with NPN type sensors)

Note that the input common (TB3 pin 12) only affects the 11
isolated inputs. it has no connection to the outputs or other
circuitry on the 7I96

The 7I96 outputs are switches, they have no power
connections, so to drive a 24V relay you would connect

+24V --> Relay_Coil+
Relay_Coil- --> OUTX+
OUTX- --> GND

You need a flyback diode across the relay coil
cathode (band) to Relay_Coil+
 
Last edit: 14 Sep 2021 20:25 by PCW.
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15 Sep 2021 06:39 #220673 by Ekholm
Yes i think i will go for the resistors and make the connections more streight forward. Thanks for the help!
I found some 2,2kohm resistors at 0,67w here at home, will they work? or should i search for higher power ones?

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15 Sep 2021 06:47 #220675 by Ekholm
if i got my calculations right
24v
R=2200ohm
=>U=R*I
I=U/R=24/2200=0,01A
P=R*I^2=2200*0,1^2=0,22W
So if i have calculated it right it will work

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15 Sep 2021 08:26 #220681 by tommylight
Looks OK, but i did not have my morning coffee yet, so do not trust me, yet.

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