I would be very careful about connecting the Renco rotary encoder directly to the PLC inputs. The best I can figure out is that the encoder outputs are either:
1. TTL compatable. Actually open collector with a pullup. 0..5 volts. "VC" version. The A and /A outputs are complimentary. You would use one or the other. You would not connect these outputs to ground 0V.
2. Differential. Same spec as modern RS-485 transceiver. "LD" version. The A and /A outputs are the differential pair for the A timing signal. You would use both signals.
If you have the TTL version you will need to convert the TTL outputs to 0..24VDC. ULN2003 is a good option. There are examples in the TriLog manuals on how to do this.
If you have the differential output version you'll need a differential receiver and then level convert this to 0..24V via a uln2003.
However, if you have connected the encoder to the PLC inputs directly, you may have not need to worry about debugging the PLC firmware. The inputs on the PLC have a pull up resistor to 24V and this voltage could damage the encoder's outputs. In this case you may need a new encoder.
This is a link to a related Renco encoder. This is about all I could find in the way of documentation. Renco is out of business and this encoder hasn't been made for a number of years.
http://www.renco.com/fileadmin/files/Productinfo/00546600.pdfGood luck,
Gary d