A classic impedance bridge. Measures resistance, inductance and capacitance. Reactances are measured at 1 kHz when using the internal oscillator, or up to 40 kHz with an external sine wave source. Quite impressive specs for the day:

  • Resistance: 1 mOhm to 11 MOhm.
  • Capacitance: 1 pF to 11 mF.
  • Inductance: 100 nH to 1100 H.

Basic accuracy ±(0.5 % + 0.1 % f.s.) at the lowest ranges. Also measures dissipation factor and quality factor.

The user adjusts the internal bridge such that the two branch impedances are balanced. This is indicated with a null meter. The user manual includes schematics and basic theory of operation.

Leader LCR-740 bridge

Selector and range multiplier.

Bridge adjustment control.

Rigid wire from binding posts to PCB. For low residual resistance.

Switches to calibrate the reference capacitance, used for both capacitance and inductance measurements.

Calibration of 0.01 Ohm range. Interesting implementation of high-power potentiometer: tracks on PCB and screw adjustment. 

Selector and multiplier switches.