3. Encoder interfaces: Incremental interfaces

3.1 TTL electronics/RS422
3.2 HTL and HCHTL electronics

3.1 TTL electronics/RS422

Incremental TTL-signals are transmitted as digital squarewave pulse trains S00 and S90, phase-shifted by 90 el°. The reference mark signal consists of one reference pulse denoted as Sref, which is gated with the incremental signals. As an option on TTL-encoders, the integrated electronics also produce inverse signals of S00 and S90 for noiseproof differential transmission. In this case the encoder signals comply with the RS422 standard.

Output signals, TTL electronics.
Image text: Output signals, TTL electronics.

Interface Square-wave TTL or
RS422 (differential)
Incremental signals S00, S90 (optional S00, S90)
Reference mark
Pulse width
Delay time
Sref (optional Sref)
90 el° (other on request)
td < 50 ns
STATUS (optional)
Pulse width
Improper function: Low
Proper function: High
ts > 20 µs
Signal level Uh > 3 V with - Ih = 10 mA
Ul < 0.4 V with Il = 10 mA
Permissible load Z0 = 100 W
Il < ±20 mA (per output)
Cload < 1000 pF
Outputs are short-circuit protected max. 1 min against 0V and +EV
Switching times
(10% to 90%)
t+/t- < 200 ns
With 1 m cable and recommended input circuitry

 

Recommended subsequent electronics, TTL / RS422.
Image text: Recommended subsequent electronics, TTL / RS422.

The permissible cable length for transmission of the TTL square-wave signals to the subsequent electronics depends on the edge separation and whether differential (6 channels) or single-ended transmission is used. Note that the permissible cable length is calculated as long as the power supply can be ensured at the encoder. Make sure to compensate for voltage drop in the power supply lines.

3.2 HTL and HCHTL electronics

Leine Linde encoders with HTL interface incorporate electronics that digitize sinusoidal scanning signals. The incremental signals are transmitted as digital square-wave pulse trains S00 and S90, phase-shifted by 90 el°. The reference mark signal consists of one reference pulse Sref, which is gated with the incremental signals. In addition, the integrated electronics produce inverse signals of S00 and S90 for noise proof differential transmission. The fault-detection signal STATUS indicates fault conditions such as under voltage of the power supply or failure of the light source. It can be used for such purposes as machine shutoff during automated production.

To prevent counting error, the subsequent electronics should be designed to process as little as 90% of the edge separation a. See diagram below.

The permissible cable length for incremental encoders with HTL signals depends on the scanning frequency, the effective power supply and the operating temperature of the encoder.

Output signals, HTL / HCHTL electronics
Image text: Output signals, HTL / HCHTL electronics.

 

Interface HTL or HCHTL
Incremental signals S00, S90 (optional S00, S90)
Reference mark
Pulse width
Delay time
Sref (optional Sref)
90 el° (other on request)
td < 50 ns
STATUS (optional)
Pulse width
Improper function: Low
Proper function: High
ts > 20 µs
Signal level Uh > 21 V with - Ih = 20 mA         
Ul < 2.8 V with Il = 20 mA
Permissible load Z0 = ±40 mA
Il < ±100 mA (per output)
Cload < 10 nF
Outputs are short-circuit protected max. 1 min against 0V and +EV
Switching times
(10% to 90%)
t+/t- < 200 ns
With 1 m cable and recommended input circuitry

 

Recommended subsequent electronics, HTL.
Image text: Recommended subsequent electronics, HTL.

The graph shows the permissible cable length at various frequences for HTL encoders.
Image text: 
The graph shows the permissible cable length at various frequences for HTL encoders.