TTL card

We have a controllogix L72 whit DHRIO card reading a PLC5 rack that which we removed processor and replaced with 1771-ASB.
the first slot is 1771-IGD the 2 next one are 1771-OGD we seem to have issue to read the encoder connected to the card.
Is there an issue in speed with processor ? comm? or there is a trick when converting from 5 to 5000?

Welcome to the PLCTalk forum community !

Yes, it takes significantly longer to scan I/O modules across a network than it does across the controller backplane. This is especially true on the legacy RIO network, compared to modern Ethernet.

Does your application use an ordinary incremental encoder, or a Gray Code type device ?

What model of PLC-5 controller occupied that chassis in the past ?

The first option I would investigate is using a modern counter module like a 1734-IJ (5V encoder POINT I/O module) to handle the encoder input.

The second option would be to re-install the PLC-5 and use it to perform just the local counts and relay that data to the ControlLogix by putting one of its channels in RIO Adapter Mode, if it's a model that has more than one RIO channel, like the PLC-5/40.

The PLC was PL5/40E
the encoder is a quadrature encoder 1000 pulses

dmarcos said:

The PLC was PL5/40E
the encoder is a quadrature encoder 1000 pulses

Click to expand...

Anyway to keep 1771-asb and read it with dhrio?

How fast does the encoder turn ?

For the sake of back-of-the-bar-napkin calculations, say it takes 10 ms to scan the RIO network.

If you have to scan twice per input pulse width to catch the leading edge and trailing edge of a pulse, then your pulses can't be shorter than 20 ms if you want to count them all. And if you want to catch both edges of a quadrature signal, the pulses would have to be twice as long, so 40 ms.

A 1000 PPR encoder will generate 40 ms pulses at just 1.5 RPM

(note that I may be thinking incorrectly of Nyquist's theorem and quadrature encoders. It's been a long day)

Not only did the PLC-5 scan the backplane an order of magnitude faster than the RIO network can, it also had a Processor Input Interrupt (PII) routine that might have been used with an encoder on a TTL input card.

I strongly recommend you plan to run the encoder to a modern input module that does counting onboard.