Hi Every body,
the other day i was looking at encoders which is connected to plc. i have never worked with encoders neither any idea how one tracks the postion of system with encoder. as i know a high speed counter module sees the inputs at every rotation from encoder.

but how do we keep the track of it in plc as systems moves in linear path. and how one resloves the position if in the middle, plc loses power supply and encoder data or counter data is lost.

i hope to get clear answers how the enocder is connected and logic is implemented in PLC in general.

thanks in advance.

 

When using an Incremental Encoder, as you have mentioned, you can lose the positional data if the power is lost. So most systems will use a homing or reference routine to establish a reference point to count the pulses from. PLC's will use high speed counter modules or inputs to count these pulse and pass this to the PLC as a positional value. An option s to use an absolute encoder, as this will give a positional value straight from the encoder, but there are limitations on the number of rotations these can do.

 

First you need to know what type of encoder you have.
1: Pulse Encoder does not have a direction it just sends a pulse to a high-speed counter module. you will have to calculate how much the device moved for one pulse.

2: Quadrature Encoder has an A & B pulse 90deg out of phase. This will tell the Quadrature Encoder module if the device is moving forward or backwards. The calculation will need to be made how much the device has moved per Rising side of A pulse and Rising side of B pulse and the falling edge of A then B pulse.

The above encodes will more than likely lose the position if the PLC is turned off and the device will have to be homed to get back to 0 position.

3: Absolute Encoder will tell you the position. Example: If this is on a rotating shaft and you are monitoring 360deg, the encoder reports back 0-359deg. If power is turned off and the device moves and power is turned on, the encoder will tell you the position where it is located. It does not loose it's position.