90589 Rev B.3 4/13
Page 3 of 12
1.0 Introduction
The P702B power unit/amplifier is a portable power source with integral signal conditioning for use with
internally amplified accelerometers. Signal conditioning includes amplification, integration and fault
indication.
2.0 Description
The P702B power unit/amplifier is a portable unit specifically designed to furnish 2.4 mA constant DC
current (+27 VDC) necessary to operate the internal charge amplifiers of Meggitt Sensing Systems and
similar piezoelectric transducers (accelerometers and velocity sensors.) In addition the P702B provides
signal conditioning, includes features such as selectable gain levels of 1, 10, 100, extremely low-noise,
integration to yield velocity output, battery condition indication, and visible overload or open/shorted cable
indication. This gives the test engineer broad capabilities for the accurate measurement and recording of
vibration signals over a wide range of test situations. Also virtually any high impedance charge-type
accelerometer can be operated with the P702B with the addition optional charge converter accessory,
CC701. The P702B also has built-in ESD protection to guard against damage of the internal electronics.
All switches and controls are on the front panel. Transducer input and output BNC connectors are
located on the rear panel, as is a connector for the optional line adapter/charger, See Figure 1 in the
appendix.
The P702BF-1 is identical to P702B, except that the frequency response of the P702BF-1 is specified as
–3 dB from 0.5 Hz to 20 kHz (versus 0.5 Hz to 50 kHz for the P702B) in acceleration mode. Other than
the high end frequency response, the P702BF-1 is identical to the P702B in terms of operation,
maintenance and troubleshooting.
3.0 Operation
3.1 Theory of operation
The P702B power unit/amplifier consists of the major circuits and components shown in Figure 2 in the
appendix. Panel functions are shown in Figure 1. The power module pr 27 VDC through an
internal 2.4 mA (other values between 2.0 and 10 mA can be furnished on request) constant current
diode to the transducer, as well as the DC excitation for the selectable gain amplifier, the fault indicator
circuit, and the integrating circuit.
The power is normally supplied from the three internal 9 volt batteries. When the optional LA704 Line
Adaptor is used, the internal batteries are automatically disconnected when the adaptor’s output cable is
plugged into the power jack on the rear of the P702B unit. See Figure 3 in the appendix for correct
jumper placement.
The vibration signal fed into the P702B Transducer input connector passes through a low pass filter
(optional) and to the first gain stage which amplifies the signal by X1 or X10 according to the gain switch
setting. The signal is split and one path is routed to an integrating amplifier to become an output signal
proportional to velocity (mV/in/sec). It then rejoins the non-integrated signal at the ACCeleration/VELocity
selector switch. When the switch is in the ACCeleration position, the signal goes directly to the second
