Operation

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 provides + 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

stage gain amplifier which can introduce an additional X1 or X10 gain. By using different combinations of

first and second stage gains, the output can be set for gains of X1. X10 or X100.