ettikudiappan
Member
We have several output module 1756-OB32 that is used to turn on 24Vdc loads. One of the load is a vision capture system that gets a trigger from the output module.
When there is an Emergency stop, the electrical wiring is done such that the 24Vdc for the output modules are cut off. Once reset, the 24Vdc power is turned ON. This 24Vc is the wet supply that is used to power the output loads like relays and commands to motor drives.
We noticed that even though in the PLC the outputs are off, the vision system got triggered when there is an Emergency stop and reset condition. That is, whenever the 24Vdc power is turned on, the vision gets triggered. Placing a multimeter on the corresponding terminal at the output module, we found that there was a spike on the output line for a very very short time, but enough to trigger digital devices like the vision system. What we believe is that since 1756-OB32 is a digital output (as compared to relay output), the transistor inside the module gets fired for a very short time and creates the spike.
Can please advice if this is normal or anything that we can do to prevent this from happening?
When there is an Emergency stop, the electrical wiring is done such that the 24Vdc for the output modules are cut off. Once reset, the 24Vdc power is turned ON. This 24Vc is the wet supply that is used to power the output loads like relays and commands to motor drives.
We noticed that even though in the PLC the outputs are off, the vision system got triggered when there is an Emergency stop and reset condition. That is, whenever the 24Vdc power is turned on, the vision gets triggered. Placing a multimeter on the corresponding terminal at the output module, we found that there was a spike on the output line for a very very short time, but enough to trigger digital devices like the vision system. What we believe is that since 1756-OB32 is a digital output (as compared to relay output), the transistor inside the module gets fired for a very short time and creates the spike.
Can please advice if this is normal or anything that we can do to prevent this from happening?