J aRCUIT SUMMARY
3.1 8RIDGE CIRCUITS
The bridge circuits used in the TF 2700 are basically those used in
other Marconi universal impedance bridges. A Wheatstone circuit is used
far re sistance measurement while inductance and capacitance are measured
by comparison with a standard capacitor in R-C ratio arm circuits. The
a. c. measurement circuits are shown functionally in Fig. 3. l.
With reference to the Circuit Diagram at the end of the handbook.
C4 is the standardcapacitor whichhas the LOSS BALANCE potentiometers,
RV4 and RV5 connected in series or in parallel with it. according to the
setting of the D -Q switch. This LOSS BALANCE arm is replaced by a 100 {"1
resistor, R12, far resistance measurements.
The RANGE resistors, associated with switch SB, consist of six
metal film high stability type, R15 to R20, and two wirewound, Rl3 and
R14.
The main BALANCE contrai comprises an eleven step switch, SC,
and a continuously variable intermediate contrai, RVI. This system gives
good readout discrimination and improved freedom from fine balance adjust-
menta being affected by coarseness of the potentiometer track. The bal-
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Fig. 3. l Functional Diagram far A. C. Measurements
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