3.2.3 Selection of encoder type. Toshiba E6580772

E6580772③

★

Caution in case of using open collector encoder connection

In case using pulse command oscillator and open collector encoder, the rise time of the voltage when the transistor is OFF tends to be longer than the fall time at the time when the transistor is ON. Therefore, if the maximum input frequency becomes higher, the pulse duty cannot maintain the 50±10% specification.

Conduct derating on the maximum input frequency so that the pulse duty will be within the following specification range.

<Derating computation formulae of open collector’s maximum input pulse frequency >

0.8／(Maximum input frequency x A) – Voltage rise time ≧ 3 x 10

–6

…..①

A : (single phase input: 2) (two-phase input: 4)

Voltage rise time ＝ Encoder exclusive pulse rise time + R x C

Encoder exclusive pulse rise time (s) : Please inquire at the encoder manufacturer.

R (Ω) (Input resistance) : internal resistance 1000(Ω)＋external resistance value

C(F) (Cable static capacity)

(In case there is external resistance)

: Please inquire at the cable manufacturer.

<Example>

Encoder

Cable

: LBJ-005-500 (SUMTAK), 2-phase input

Encoder pulse rise time : 0.35 x 10

-6

(s)

: ROVV-SB-0.2-5P-10m (Furukawa Electric Co., Ltd)

Static capacity : 120 x 10

–12

(F/m) x 10 (m)

From Formulae①

0.8／(Maximum input frequency x A) – Voltage rise time ≧ 3 x 10

–6

Voltage rise time = (0.35 x 10

–6

) + 1000 x (120 x 10

-12

x 10)

= 1.55 x 10

-6

[Maximum input frequency] ≦87912 (Pulse/s) [Single phase input]

≦

43956 (Pulse/s) [Two-phase input]

3.2.3 Selection of encoder type

The encoder type should be selected, following the table below.

Encoder Type

Complementary

Open Collector

Characteristics

Rated voltage output with emitter/follower combination.

High anti-nose characteristics. High-speed response.

Long-distance transmission capability.

Need to pay attention to waveform irregularity.

The collector of the transistor is output directly.

Low anti-noise characteristics. Low-cost.

Need to pay attention to waveform irregularity and distortion.

Maximum Wiring Length

１００ｍ

１０ｍ

18