Functions; Acquisition Of Encoder Signals; Position Input With Ssi Absolute Encoder - Siemens SIMATIC ET 200SP Manual

Product overview

2.2 Functions

2.2 Functions
2.2.1

Acquisition of encoder signals

2.2.1.1

Position input with SSI absolute encoder

You can use the TM PosInput 1 technology module with an SSI absolute encoder for
position input. The technology module reads the position via a synchronous, serial interface
from the SSI absolute encoder and sends it to the controller.
You can switch the digital outputs of the technology module exactly at defined position
values, independently of the user program. Position input with an SSI absolute encoder does
not involve gate control.
Gray-dual conversion
Gray-code and dual-code SSI absolute encoders are supported.
Range for position value
You can specify a frame length of 10 bits to 40 bits for the SSI absolute encoder. The
configurable bit numbers of the LSB and the MSB of the position value in the frame define
the value range. The technology module can read in a position value with a maximum length
of 31 bits and transfer it to the PLC. The position value is treated as unsigned positive value
and can assume values between 0 and 2
Complete SSI frame
Instead of having a measured variable returned, you can choose to have the least significant
32 bit of the current unprocessed SSI frame returned. This provides you with encoder-
specific additional bits, such as error bits, in addition to the position value. If the SSI frame is
shorter than 32 bits, the complete SSI frame is returned right-aligned and the top unused bits
are returned with "0" in the feedback interface.
Capture (Latch)
You can save the current position value as Capture value using the edge of the digital input.
The Capture function is triggered by rising, falling or both edges.
Hysteresis
You can specify hysteresis for the comparison values, within which a digital output will be
prevented from switching again. An encoder can come to a standstill at a specific position,
and slight movements may make the position value fluctuate around this position. If a
comparison value or a position value limit lies within this fluctuation range, the corresponding
digital output is switched on and off with corresponding frequency if hysteresis is not used.
The hysteresis prevents these unwanted switching operations.
14
-1.
(MSB-LSB+1)
Technology module TM PosInput 1 (6ES7138-6BA00-0BA0)
Manual, 04/2016, A5E33015755-AC