Specifications

IP 240 Position Decoding
The zero offset value thus always offsets the zero point of the actual value range to the reference
point. A zero offset can be revoked by transferring a ”0” value to the IP. Configuring FB 169 does
not transfer the zero offset entered in the DB.
Configuring FB 169 does not transfer the zero offset entered in the DB.
• ”Set actual value” at the software level
With the following sequence of instructions, you can assign a specific actual value to the
current location by transferring two zero offsets:
write the negated new setpoint actual value as zero offset,
read the actual value,
invert the sign of the actual value,
write this negated actual value as new zero offset,
read the actual value and compare it with the setpoint actual value.
This software-based method of setting an actual value may be used only when the actual
value does not change between ”Read actual value” (step 2) and ”Write new zero offset”
(step 4).
Failure to observe this rule will cause the location of setpoint actual value to vary with the
traversing speed and the response time until the new zero offset has been written. An
additional zero crossing or actual value overflow would then produce a completely falsified
new actual value.
7.2.2 Resolution
Resolution can be increased by configuring a pulse multiplication. To do this, enter the desired
resolution in parameter AFL in configuring FB 169 ( Section 7.3.1).
The precision of the displacement distance decoded can be improved by doubling or quadrupling
the resolution. The available traversing range is reduced by factor 2 or 4.
Fig. 7-3. Evaluating the Encoder Pulses
2nd increm.1st increm.
Increment1st 2nd 3rd 4th
1st increment
Encoder pulse train A
Encoder pulse train B
Single resolution (AFL=1)
Encoder pulse train A
Encoder pulse train B
Twofold resolution (AFL=2)
Encoder pulse train A
Encoder pulse train B
Fourfold resolution (AFL=4)
EWA 4NEB 811 6120-02a 7-3