Heathkit Model IB-1B

Impedance Bridge

Calibration Procedure

· The meter pointer should be on the center zero of the meter scale.  If the pointer is not over this mark, adjust the zero-adjust screw at the bottom of the meter until the pointer is properly aligned.

Ancillary Equipment Needed

Frequency Counter

550-ohm 1% resistor

· Mount the 1% resistor on a dual banana plug to use as a calibration standard.

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OSCILLATOR ADJUSTMENT

(    )         Set the GENERATOR LEVEL control maximum clockwise. Allow the tubes to come up to operating temperature.

 (    )        Set the GENERATOR SELECTOR switch to the AC INT position.

(    )         Set the DETECTOR switch to the AC INT position.

(    )         Set the FUNCTION switch to the L-DQ position.

(    )         Set the RANGE switch to the 1h position on the L scale.

(    )         Connect a frequency counter to the top UUT (unit-under-test) terminals.

(    )         Adjust the trimmer capacitor control G [chassis] (see Figure 5) until the counter reads 1000 Hz.

(    )         Disconnect the frequency counter from the UUT terminals.

Front Panel Initial Conditions

(    )         Set the FUNCTION switch to the R position.

(    )         Set the GENERATOR switch to DC INT position.

(    )         Set the DETECTION switch to DC SHUNT position.

(    )         Set the RANGE switch to the 100 ohms position on the R scale.

(    )         Set the outer ring of CRL control [large set of dials, right side of panel] to the center of the 5 position on the dial at the pointer position.

(    )         Set the GENERATOR LEVEL control to minimum counter-clockwise, not to the AC OFF position.

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CRL CALIBRATION

(    )         Connect a 550-ohm 1% resistor to the UUT terminals.

(    )         Set the GENERATOR LEVEL control maximum clockwise.

· The DC METER position is spring loaded and will automatically return to the DC SHUNT position.

(    )*       Adjust the inner CRL control only until the meter does not change when the DETECTOR switch is rotated to the DC METER position.

(    )*    Loosen the inner CRL control knob only and rotate it till the two dials read 5.5 at the pointer position.

(    )*    Tighten the inner CRL control knob.

(    )         Repeat the above thee steps* until the meter does not move when the DETECTOR switch is rotated to the DC METER position.

(    )         Set the GENERATOR LEVEL control counter-clockwise to the AC OFF position.

(    )         Disconnect the 550-ohms 1% resistor from the UUT terminals.

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DQ CALIBRATION

· If greater accuracy of the DQ control [large dial, left side of panel] is desired (more than that obtained by simply zero-setting the knob), perform the following steps:

(    )         Set the front panel initial conditions as described in the OSCILLATOR ADJUSTMENT section.

(    )         Temporarily disconnect the end of the wire connecting lug 2 on the rear section of the DQ control to lug 6 on the rear deck of the FUNCTION switch FS (see Figure 10).

(    )         Temporarily connect a jumper wire between lug 1 of the rear section of the DQ control to lug 1 [rear UTT terminal (black)] of the terminal strip TS on top of the bridge (see Pictorial 2).

(    )         Temporarily connect a jumper wire between lug 2 of the rear section of the DQ control to lug 2 [front UTT terminal (red)] of the terminal strip TS on top of the bridge (see Pictorial 2).

· These temporary connections can be wired through a set of chassis mounted toggle switches enabling ease of future DQ adjustments.

(    )         Set the GENERATOR LEVEL control maximum clockwise. Allow the tubes to come up to operating temperature.

(    )         Set the CRL controls to read 160 ohms.

(    )         Adjust the DQ/Q control until the meter reads 0 (near the 0.1 mark on the D-Q knob scale).  This is a CRITICAL adjustment.

(    )         Verify the adjustment by turning the DETECTOR switch to the DC METER position. No meter pointer movement should be noticed at exact zero.

(    )         When the bridge is balanced, note the position of the 0.1 mark on the DQ dial with respect to the pointer.

(    )*       Correct the DQ knob dial setting to read exactly 0.1.

(    )*       Rebalance the bridge and check the dial setting.

(    )         Repeat the above two steps* until no change is recorded.

(    )         Set the RANGE switch to 1000 ohms as a double check. The bridge should balance at 1.0 with the DQ dial.

(    )         Set the GENERAL LEVEL control to AC OFF position.

(    )         When the DQ calibration procedure is complete, remove the temporary jumpers and reconnect the proper leads to the DQ control and the FUNCTION switch.

(    )         Calibration procedure is complete.