Specifications

IP 240 Position Decoding

7 Position Decoding

7.1 Application

In this mode, the IP 240 can be used in all applications in which position changes are to detected

and decoded using incremental encoders. The module can process encoder pulse trains with a fre-

quency of up to 500 kHz for symmetrical encoders and 100 kHz for asymmetrical encoders.

The function of a cam controller can be simulated by presetting reference tracks. Error detection

during signal acquisition is possible by monitoring signals.

7.2 Principle of Operation

For the position decoding mode the following STEP 5 blocks are necessary:

• A data block

You must create a data block (DB) prior to calling the configuring function block for the first

time. New data must be entered in this DB prior to its transfer to the IP 240 by the FB 170.

Data that is read from the IP 240 is stored in this DB by control FB 170.

• Configuring FB 169

You structure one or both channels of the IP 240 in position decoding mode with configuring

FB 169. The configuring FB is normally called in the restart OB.

• Control FB 170

The

control FB 170 is called in the cyclic program or the interrupt program. By means of the

FB parameter FKT, you

can specify whether data is to be read from or transferred to the IP 240.

7.2.1 Actual Value

Formation of the actual value

An internal, signed count is determined by counting the pulses and evaluating the phase

displacement between encoder pulse trains A and B. The actual value IST is obtained from this

count by addition with the definable zero offset NVER.

Counting direction

The IP 240's encoder pulse count is

• an up count when the B signal is the leading signal.

• a down count when the A signal is the leading signal.

In IP 252 expansion mode, a leading A signal corresponds to a positive speed.

Fig. 7-1. Counting Direction in Positon Decoding Mode

A signal

B signal

”Up” counting ”Down”counting

EWA 4NEB 811 6120-02a

7-1