Bird Technologies 4314B - Manual (Page 18)

6
Peak Power Operation
The Model 4314B is designed to measure peak power in addition to average
power. When the toggle switch is placed in peak mode, battery power energizes
the amplifier system. If the AC adapter is being used, it energizes relay (K1) and
disengages the batteries (Figure 3 on page 8).
The battery test circuit is energized when the push button of switch S2 is
depressed. If the voltages of the two 9 V batteries are within the limits necessary
to properly operate
the amplifier circuit, the pointer of the meter deflects beyond the battery test
mark on the meter scale. If the pointer fails to reach the mark, the batteries
need replaced. Replacement of both batteries simultaneously will assure that
sufficient battery power will be available for extended periods of time (see
“Maintenance” on page 21).
The amplifier circuit is designed to provide current to the meter which indicates
at a steady state the peak of the power applied to resistor R5. Resistor R5 exactly
matches the resistance of meter M so that the existing circuit in the Plug-In Ele-
ment is loaded exactly the same as during the average reading mode (Figure 2
on page 7).
When switch S1 is pressed, the DC input which is normally applied to the meter
is interrupted and is applied instead to resistor R5 and differential amplifier Q1.
This results in a current gain ratio of approximately 100:1. This output is applied
to a resistance bridge consisting of resistors R6, R7, R8, R9, and R10. Variable
resistor R8 of this bridge permits zero calibration of the amplifier circuit. Bridge
output is applied to differential amplifier U1 which provides a voltage gain of
about 1000:1. This ratio represents the surge of voltage from the amplifier
which charges capacitor C3 and indicates the minimum pulse duration. Capaci-
tor C3 applies a potential to differential amplifiers Q2 and Q3 as long as the
capacitor remains charged. These amplifiers provide a massive current gain
ratio, but unity or slightly less voltage gain. This is applied to meter M to indicate
the peak power in the line. A portion of the DC output of amplifiers Q2 and Q3 is
fed back to resistor R4 and to amplifier Q1. Resistor R4 is matched to resistor R5
to provide unity gain to the amplifier. This feedback circuit maintains the output
from Q1 and U1 to keep capacitor C3 charged to that value which yields unity
closed loop gain.
The capacitor continues to energize Q2 and Q3, to maintain the reading of the
meter even though the peak of the pulse is no longer applied to the amplifier
assembly input. Only the peak power is indicated even though there is a wide
fluctuation of input power.
Because of capacitor leakage, diode back resistance, and transistor input cur-
rent, there will be a decay in the circuit that limits the time the amplifier system
will retain its output level. As the circuit decays, the meter will return to zero if
no additional pulses are received at resistor R5.