Hello,
We have systems that are 24VDC positive ground with negative signal as PLC inputs. Every once in a while we get this question as to why we are set up this way. No one knows the exact answer. However, we have gone so far along that all spare parts like PLC input cards, output cards, sensors etc. are stocked. It could be expensive and at times, confusing to change this system. Can some one point out the advantages or history of why a negative logic system could have been started? I am very interested to know.
Regards,
lquadros.
We have systems that are 24VDC positive ground with negative signal as PLC inputs. Every once in a while we get this question as to why we are set up this way. No one knows the exact answer. However, we have gone so far along that all spare parts like PLC input cards, output cards, sensors etc. are stocked. It could be expensive and at times, confusing to change this system. Can some one point out the advantages or history of why a negative logic system could have been started? I am very interested to know.
Regards,
lquadros.