Meggitt vibro-meter SpeedSys300 ODS301, Руководство пользователя, Страница: 138 / 170

USER MANUAL Document reference MAODS301/E
SpeedSys300 ODS301 overspeed detection system Edition 4 - May 2022
D - 8
I am using the frequency (speed) output but cannot see an output signal. What
APPENDIX D: FREQUENTLY ASKED QUESTIONS (FAQ)
D.6 I am using the frequency (speed) output but cannot see an output signal.
What should I check?
The SpeedSys300 ODS301 module’s frequency (speed) output features an open-collector
output signal in order to support interfacing to different devices that have different operating
voltage levels.
Accordingly, the frequency (speed) output signal requires a pull-up resistor connected to the
required voltage level. If a pull-up resistor is not used, the frequency (speed) output will only
appear as a low-level signal (of the order of 100 mV).
Examples
When interfacing to an external system, the value of the pull-up resistor can be calculated as
follows:
R = V / I
R
PULL-UP
= V
SUPPLY
/ I
MAX
NOTE: The SpeedSys300 ODS301 overspeed detection system data sheet specifies a
maximum voltage of +24 V
DC
and a maximum current of 100 mA for the frequency
(speed) output.
So, when interfacing to an ex24 V
DC
system:
R
PULL-UP (MIN)
= +24 V
DC
/ 100 mA = 240 Ω (min.)
So, when interfacing to an ex5 V
DC
system:
R
PULL-UP (MIN)
= +5 V
DC
/ 100 mA = 50 Ω (min.)
In practice, 10 or 1 kΩ is often a good starting choice if you are unsure of what resistor value
to try.
See 2.2 SpeedSys300 ODS301 module connectors for further information on the
SAFETY ANALOG / FREQ OUT connector.