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V 50/60 Hz for the LA704-220). Internal batteries of the P702B are now disconnected and the unit is
operated from the power line.
Note
: The tests above apply whenever the unit is powered by its internal batteries (Alkaline or NI-CD) or
from the line adaptor.
4.3 FAULT monitor
If the FAULT monitor signal light glows red (after the 20 second warm-up period), the measurement
system should be carefully checked to see if any of these seven conditions exist:
Accelerometer is not connected
Accelerometer has internal open connection
Accelerometer has internal short.
Cable assembly has internal connection (break)
Cable assembly has internal short
Accelerometer’s internal amplifier is overload
Optional charge converter (CC701) is malfunctioning/overloaded
If none of these faults appear to be present, but the fault monitor continues to glow, the easiest way to
check is to substitute another P702B unit (known to be in good working condition) in the measurement
system. If this restores proper operation, the original P702B is malfunctioning and should be returned to
the factory for repair.
4.4 Electrical calibration
The validity of the measurements performed by the vibration measurement system depends on the
continuing proper function of the P702B power unit/amplifier. We recommend that an electrical
calibration of the measurement system be performed regularly (once a year) or before any extensive
series of vibration measurements.
An electrical signal should be substituted for the accelerometer signal for the purpose of calibration. The
output of a sinusoidal signal generator at a recommended frequency of 100 Hz is fed through an RC
network into the TRANSDUCER input connector of the P702B. This network consists of a 100 MF
capacitor in series with the input, and a 4.7 K
Ω resistor across the input. The signal generator is set to
produce an output signal amplitude of 1 V rms On the P702B and will vary according to GAIN switch
setting. To verify gain, divide the voltage at the P702B’s output BNC by the voltage at the P702B’s
TRANSDUCER input BNC.
See Figure 4. The P702B may also be returned to Meggitt Sensing Systems for recalibration.
