HEIDENHAIN PWM 20 - Manual (Page 218)

November 2014 Interface description 219
Possible specifications
7.3.2 Incremental signals HTL (HTLs) square-wave interface
HEIDENHAIN encoders with HTL interface incorporate electronics that digitize sinusoidal
scanning signals with or without interpolation.
The incremental signals are transmitted as the square-wave pulse trains Ua1 and Ua2, phase-
shifted by 90° elec. The reference mark signal consists of one or more reference pulses Ua0,
which are gated with the incremental signals. In addition, the integrated electronics produce
their inverted signals Ua1, Ua2 and Ua0 for noise-proof transmission (does not apply to HTLs).
The illustrated sequence of output signals – with Ua2 lagging Ua1A – applies for the direction of
motion shown in the dimension drawing.
The fault-detection signal UaS indicates fault conditions such as failure of the light source.
It can be used for such purposes as machine shut-off during automated production.
The measuring step results from the spacing between two edges of the signals Ua1 and Ua2
by 1-fold, 2-fold or 4-fold evaluation.
The subsequent electronics must be designed to detect every edge of the square-wave pulses.
The minimum edge separation a stated in the specifications refers to a measurement at the
output of the given differential input circuit. To avoid counting errors, the subsequent electronics
should be designed such that it can operate with 90% of the edge separation a.
The maximum permissible shaft speed or traversing velocity must never be exceeded.
Interface Square-wave signals HTL/HTLs
Incremental signals Two HTL square-wave signals Ua1 and Ua2 and their
inverted signals Ua1, Ua2 (HTLs without Ua1, Ua2)
Reference mark signal
Pulse width
Delay time
One or more HTL square-wave pulses Ua0 and their
inverse pulses Ua0 (HTLs without Ua0)
90° el. (other widths available on request)
|t
d
| 50 ns
Fault detection signal
Pulse width
One HTL square-wave pulse UaS
Improper function: LOW
Proper function: HIGH
t
S
20 ms
Signal level U
H
21 V with
I
H
= 20 mA with power supply
U
L
2.8 V with I
L
= 20 mA Up = 24 V, without cable
Permissible load |I
L
| 100 mA max. load per output, (except UaS)
C
load
10 nF with respect to 0 V
Outputs short-circuit proof max. 1 min. to 0 V and Up (except
UaS)
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