Toshiba G7 - Manual (Page 20)

G7 ASD Multi-Protocol Communication Option and PG Feedback Option Manual 13
6.5 Maximum Input Frequency Using an Open
Collector Encoder
When using an open collector (pulse input type 2) encoder, the rise time of the voltage when the
encoder’s internal transistor turns OFF tends to be longer than the fall time when the transistor turns
ON. Therefore, if the input frequency becomes high enough, the pulse duty cycle cannot maintain the
50±10% specification. For the pulse duty cycle to be within the specified range, the generated
frequency from the open collector encoder needs to be below a maximum input frequency. To calculate
the maximum input frequency for an open collector (pulse input type 2) encoder, use the following
equations:
(eq.1) (s) 10 3 time(s) rise Voltage
A (Pulses/s) frequency input Maximum
0.8
6 − Ч = −
Ч
Single phase input: A=2
Two phase input: A=4
(eq.2)
( )
C x R time rise pulse exclusive Encoder time rise Voltage + =
Encoder exclusive pulse rise time (s) ............ Refer to encoder specifications.
R (Ω) (Input resistance)................................. internal resistance 1000 (Ω) + external resistance
value (if there is external resistance).
C (F) (Cable static capacitance) .................... Refer to cable specifications.
Example
Encoder ...........LBJ-005-500 (SUMTAK), 2-phase output, pulse rise time= 0.35 x 10 -6 (s)
Cable ...............Any Brand
Static capacitance=120 x 10 –12 (F/m) x 10 (m)
Using equation (eq.2)
Voltage rise time = Encoder exclusive pulse rise time + (R x C)
= [0.35 x 10 -6 (s)] + [1000 (Ω) x 120 x 10 –12 (F/m) x 10 (m)]
= 1.55 x 10 –6 (s)
Using equation (eq.1)
(s) 10 3 time(s) rise Voltage
A (Pulses/s) frequency input Maximum
0.8
6 − Ч = −
Ч
Maximum input frequency = 87912 (Pulse/s) for single phase input
= 43956 (Pulse/s) for two phase input