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Vision V120 transistor output - external current

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maybe this will be a stupid question, but I don't want to burn something.

I have a Vision 120 with transistor outputs, two of the outputs are turning on two relays.

The relays have a common 0V and then the +VO from the PLC.

If I connect a switch using the same +VO to manually control the relays, do I have to put a diode

on the wire coming from the PLC? or there is no problem if current comes backwards?

There is also the possibility that the output will turn on while using the manual switch is this a problem?


Thank You.

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Hi Nkwi

It is always a good idea to include diodes in this type of system. Provided you have included the appropriate diodes for your system you will be protecting the system from the inverse voltage. This will also be the same type of protection if both the manual switch and transistor are both firing at the same time, the diode will prevent a detrimental condition if you do not exceed the PIV value for ht diode
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The diodes will be connected in series with the outputs, the connection parameter, additional equipment and methods to connect will be in accordance with the electrical code in your region. The diode should be sized to handle the maximum inverse voltage. Any type or size will function provided it is for DC and the PIV is above maximum voltage expected on the line. 

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