Siemens TM PosInput1 and absolute encoder

Hello everybody!

I have following equipment

• TM PosInput1 (6ES7138-6BA00-0BA0) to read the encoder pulses
• Baumer absolute encoder (EAM580-BAC.7L4G.12130.A-11206897)

First time I thought that there is something wrong with encoder, because we run the machine and pulses read were like random: 1000, 3498, 7820, 4000,234, 2500 and so on.

Then I disconnected the encoder and connected directly to the card. Rotating it by hand, I saw that pulses were going from X to 8192, then 8192 to 0, 0 to 8192.
One rotation is 4096 pulses.

• Frame length: 25
• Bit number LSB of position value: 0
• Bit number of MSB position value: 12

Hi there,

I think you are missing the difference between frame lengt, and LSB/MSB.

How to set the frame length, as well as LSB and MSB is defined by the encoder you have, so this is nothing that can be varied.

The frame length is the length of bits the encoder provides via the SSI telegram. This has to be set correctly at the module, so that it can read out the encoder correctly. If this is not set correctly, you will have issues redaing the encoder, as after each frame length a pause is made on the clock signal, which would be done at the wrong place when setting a wrong frame length. I would usually then expect a diagnostic message from the module (if diagnostics are enabled) that states an issue with the SSI telegram, but some encoders are also very tolerant about this, so this depends.

Perhaps the explanation and examples here make this more clear: https://support.industry.siemens.com/cs/de/de/view/59709820/108269126667?dl=en
There you can see the connection between frame length and LSB/MSB.

So what you need to do is to set the correct frame length (as defined by your encoder), then with LSB and MSB define where in this frame length the position value is. Some encoders provide additional bits, and with setting LSB and MSB you define where in the SSI frame the position value is, so that the module can then only look at this and not look at the additional status bits (e.g. parity bit).

Regards,
daviso