6-3
6 Fault Diagnosis
6.3 No Measurement Signal
If the laser beam is emitted but there is no measurement signal, check the
following:
Signal level
display
1. Put a piece of reflective film at an optimal stand-off distance according to
in the beam path. Focus the laser
beam on the reflective film. Does the signal level display react ?
If the signal level display does not react, the input section of the
controller is faulty.
Now check the output signals of the controller as follows:
Velocity
signal
2. Connect an oscilloscope to the BNC jack VELOCITY OUTPUT on the
front of the controller. Does the output signal react to the movement of the
reflective film ?
3. If the output signal does not react, check whether a significant DC offset is
present.
Normally a DC voltage of less than ± 20 mV can be measured.
4. Set the oscilloscope to 1 V / DIV and block the laser beam. Is the output
signal noisy or is a straight line shown ?
Noise must occur when the laser beam is blocked.
Displacement
signal
(optional)
5. Connect the oscilloscope to the BNC jack DISPLACEMENT OUTPUT on
the front of the controller. Does the output signal react to the movement of
the reflective film ?
Now check the internal operating voltages of the vibrometer as follows:
Internal
operating
voltages
6. Switch off the controller by turning the key switch to position O.
7. Disconnect the cable to the sensor head from the back of the controller.
8. Using a multimeter, measure the internal operating voltages at the Sub-D
jack INTERFEROMETER.
shows the pin configuration of the
jack. The following voltages must be measurable with a tolerance of
±
0.2 V at the individual pins referred to GND.
Pin No.
Voltage
1, 4, 7, 8 and 15
GND
3, 6 and 9
+ 16.0 V
2
+ 5.0 V
13
- 5.2 V
5 and 10
- 15.0 V
