2 OPERAnON
2.1 GENERAL
The operational controls of this bridge are arranged to provide an
easy to use, direct reading measurement system. Fig. 2.3 summarizes
the control functions. (See page lO.)
l.l.l BALANCING THE BRIDGE
NormaI balancing procedure entails adjusting the main BALANCE
controls, in conjunction with the LOSS BALANCE control for reactive
components, in arder to bring the meter to as near zero de£lection as pos-
sible. The SENSITIVITY control allows the detector sensitivity to be red-
uced for a clearer meter indication of approaching balance with components
of unknown value.
The meter de£lection will always be to the right of zero for a. c.
measurements; but ford.c. resistance measurements it will swing through
zero as the balance point is passed so that when the de£lection is to the left
of zero the value of the unknown is higher than the setting of the bridge and
vice versa.
Failure to obtain a complete balance null during a. c. measurements
may be for one or more of the foliowing reasons:
R Too much stray capacitance or inductance.
C and L Incorrect adjustment of the LOSS BALANCE partic-
ularlyat low Q or high D sett_ings. This may be due
to the limited resolution of the contrai at Q lese than
l. Alternatively it may mean that the loss of the
test component is too complex to be simply resolved
by either series or paralielloss balance. This could
mean that it is frequency conscious so that the balance
point for the harmonic content of the a. f. source is
different tram that of the fundamental. Any external
a. f. signal used to energize the bridge should there-
fore be free tram harmonics and mains hum; it may
be necessary to use an external frequency selective
detector, connected between the DET +VE and -VE
(chassis) terminals.
C, L and R Pick up of interference, e. g., mains hum, by the
test component or its connections, see Section l.3.
Check for pick up by inserting an open circuit jack
plug in the EXT A. C. socket when the meter indic-
ation should fali to zerG.
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