Heathkit model IM-16

Solid-State Voltmeter

 

Date Calibrated:   _____/_____/_____

 

Calibration Procedure

 

•         With the meter off, the meter pointer should be over the zero indication on the meter face.  If it is not, turn the mechanical zero-adjust screw at the bottom of the meter until the pointer is properly aligned.

 

•         Install fresh batteries matching the + markings screened on circuit board.

 

*    The 9-volt battery is required for portable operation.

 

Ancillary Equipment Needed

 

AC VTVM (optional)

1.5 volt C cell (fresh) or

0.5 volt reference voltage

 

* * * * * * *

INITIAL CONDITIONS SETUP

Refer to Figures 1 and 2.

 

(    )         Set the POWER switch to the OFF position

 

(    )         Set the FUNCTION switch to the DC+ position.

 

(    )         Set the VOLTS switch to the 0.5 position.

 

(    )         Set the OHMS switch to the R x 1 position.

 

(    )         Adjust the OHMS * control (R-17) to maximum counter-clockwise.

 

(    )         Adjust the ZERO ADJUST * control (R-19) to center of rotation.

 

*    Both the OHMS and the ZERO adjust controls have 10-turn planetary drives.

 

(    )         Set the BIAS ADJ control (R-18/20) (on circuit board) maximum counter-clockwise.

 

(    )         Set the DC CAL control (R-26) (on circuit board) maximum counter-clockwise.

 

(    )         Set the AC CAL control (R-25) (on circuit board) maximum counter-clockwise.

 

(    )         Insert the test leads phone plug into the input jack.

 

(    )         Set the test probe tip selector switch to the DC position.

 

(    )         Connect the test probe tip to the common test lead.

 

ELECTRICAL ZERO ADJUSTMENT

 

(    )         Connect the line cord to the AC power outlet.

 

(    )         Set the POWER switch to the LINE position.

 

(    )         The meter should deflect off-scale to the left.

 

(    )         Adjust the BIAS ADJ control (R-18/20) (on circuit board) for a zero meter indication.

 

(    )         Set the FUNCTION switch to the DC– position.

 

(    )         Adjust the ZERO ADJUST control (R-19) fully clockwise.

 

(    )         Meter should read approximately 1.5 on the black 15 volt scale.

 

(    )*       Adjust ZERO ADJUST control (R-19) counter-clockwise for a zero meter indication.

 

(    )*       Alternate the FUNCTION switch between the DC+ and DC– positions.

 

(    )         Repeat the above two marked steps* until no change in the meter indications.

 

DC CALIBRATION

 

·         The DC calibration of the Voltmeter can be made with a fresh C cell. However, if a highly accurate voltmeter or a dependable 0.5 volt reference voltage is available, calibration accuracy may be improved.

 

(    )         Set the FUNCTION switch to the DC+ position.

 

(    )         Set the VOLTS switch to the 1.5 position.

 

(    )         Adjust the ZERO ADJUST control (R-19) for a zero meter indication.

 

(    )         Disconnect the common test lead from the test probe tip.

 

(    )         Set the test probe tip selector switch to the DC position.

 

(    )*       Touch and hold the common test lead to the negative end of the C cell.

 

(    )*       Touch and hold the test probe to the positive terminal of the C cell.

 

*    Hold the test leads on the cell while making this adjustment.

 

(    )         Adjust the DC CAL control (R-26) (on circuit board) until the meter pointer rests over the red dot at the right side of the 15 volt scale.

 

(    )*       Remove the test probe tip from the C cell.

 

(    )*       Adjust the ZERO ADJUST control (R-19) for a zero meter indication.

 

(    )         Repeat the above four marked steps* until no change in the meter indications.

 

AC CALIBRATION

 

·         CAUTION:  Use extreme care when measuring the AC line voltage, or any high voltages.  Personal shock or instrument damage could result from carelessness.

 

·         If a more accurate AC voltage is available than the AC power line, it should be used for the AC calibration.

 

·         An AC VTVM of known accuracy can be used as a reference instrument to calibrate this voltmeter.

 

·         Modern single phase house wiring has polarized outlets.  If wired correctly, the taller slot is the white wire or low side of the power line, while the smaller slot is the black wire or hot side of the line.

 

·         CAUTION:  Use an insulated handle screwdriver while performing any of these AC adjustment methods.

 

(    )         Set the test probe tip selector switch to the AC-OHMS position.

 

Using the AC power line voltage

 

(    )**      If the unit is wired for 120 VAC operation, set the VOLTS switch to the 150 position.

 

(    )**      If the unit is wired for 240 VAC operation, set the VOLTS switch to the 500 position.

 

Method 1 - using the meter’s internal AC line voltage as a source

 

(    )         Set the POWER switch to the OFF position.

 

(    )         Disconnect the unit’s line cord from the AC power line – DO NOT JUST TURN IT OFF!!!

 

•         Make these test lead connections to the voltmeter’s transformer primaries.

 

(    )         Connect the common test lead to the low side (white) of the AC line cord.

 

(    )         Connect the test probe tip to the high side (black) of the AC line cord.

 

(    )         Connect the voltmeter’s line cord to the AC power line.

 

(    )         Set the POWER switch to the LINE position.

 

(    )         Adjust the AC CAL control (R-25) (on the circuit board) for a meter indication of the known AC voltage value.

 

(    )         Set the POWER switch to the OFF position.

 

(    )         Disconnect the unit’s line cord from the AC power line – DO NOT JUST TURN IT OFF!!!

 

(    )         Disconnect the test leads from the transformer primary.

 

(    )         Re-connect the unit to the AC power line.

 

(    )         Set the POWER switch to the LINE position.

 

(    )         Proceed down to the OHMS ADJUSTMENT section.

 

Method 2 - using an extension cord from the AC power line

 

•         This method can be performed most conveniently by using a polarized extension cord.

 

•         CAUTION:  Make sure the extension cord is NOT plugged into the AC power line first.

 

(    )      Attach the common test lead to the metal shank of a screwdriver.

 

•         CAUTION:  DO NOT TOUCH THE METAL SHANK OF THE SCREWDRIVER.

 

(    )      Insert the blade of the screwdriver into the low side of the extension cord socket.

 

•         If using this method with a polarized cord, insert the screwdriver blade into the larger slot (low side of the AC power line).

 

 (    )     Insert the test probe tip into the other extension cord slot.

 

•         CAUTION: TAKE CARE NOT TO TOUCH THE TIP OF THE TEST PROBE TO THE SCREWDRIVER.

 

(    )         Connect the extension cord to the AC power line.

 

(    )         Adjust the AC CAL control (R-25) (on the circuit board) for a meter indication of the known AC voltage value.

 

(    )         Unplug the extension cord from the AC power line.

 

(    )         Disconnect the screwdriver and the test leads from the extension cord.

 

(    )         Proceed down to the OHMS ADJUSTMENT section.

 

Method 3 – using an external AC voltage source

 

(    )         Set the VOLTS switch to the range setting matching the calibration voltage being used.

 

(    )         Connect the common test lead to the low side of the AC voltage source.

 

(    )         Connect the test probe tip to the high side of the AC voltage source.

 

(    )         Adjust the AC CAL control (R-25) (on the circuit board) for a meter indication of the known AC voltage value.

 

(    )         Turn off the AC voltage source before disconnecting the test leads.

 

(    )         Proceed down to the OHMS ADJUSTMENT section.

 

Method 4 – Using a calibrated AC voltmeter as a reference

 

(    )         Measure the AC voltage being used with a calibrated AC voltmeter and record the reading.

 

(    )         Set the VOLTS switch to the range setting matching the calibrated AC voltmeter’s reading.

 

(    )         Measure the AC voltage and adjust the AC CAL control (R-25) until the meter indicates the same value as the calibrated AC voltmeter’s reading.

 

(    )         Turn off the AC voltage source before disconnecting the test leads.

 

OHMS ADJUSTMENT

 

(    )         Set the OHMS switch to the R x 1 Meg position.

 

(    )         Set the test probe tip selector switch to the AC-OHMS position.

 

(    )*       Adjust the OHMS ADJUST control (R-17) for a full scale (INF) reading on the green scale.

 

(    )*       Touch the test probe tip and the common lead together – this should indicate a near zero indication.

 

(    )*       Adjust the ZERO ADJUST control (R-19) (with the test leads touching) to produce a zero meter indication.

 

(    )*       Separate the two test leads – the meter should return to full scale (INF) reading.

 

(    )         Set the test probe tip selector switch to the DC position.

 

(    )         Touch the test probe tip and the common lead together – this should produce an indication of approximately 1 on the ohms scale.

 

(    )         Set the OHMS switch to the R x 100K position.

 

(    )         Touch the test probe tip and the common lead together – this should produce an indication of approximately 10 on the ohms scale.

 

(    )         Set the RANGE switch to the R x 1 position.

 

(    )         Touch the test probe tip and the common lead together – this should produce an indication of approximately zero on the ohms scale.

 

•         This is the normal condition, and this test lead resistance should be considered in critical low resistance measurements.

 

(    )         Set the test probe tip selector switch to the AC-OHMS position.

 

(    )  (    )    Set the SELECTOR switch to each of the other six resistance ranges.  Repeat the above four marked

(    )  (    )    steps* for each Selector switch setting until no change in the zero indication.

(    )  (    )

 

•         Each range should give a zero indication with the test probe tip and the alligator clip touching – and an INF reading with the test leads apart. The OHMS ADJUST and the ZERO ADJUST controls may both need to be adjusted.

 

FINAL BIAS ADJUSTMENT

{Required for battery operation only.}

 

(    )         Set the test probe tip selector switch to the AC-OHMS position.

 

(    )         Set the FUNCTION switch to the DC+ position.

 

(    )         Set the VOLTS switch to the 0.5 position.

 

(    )         Touch the test probe tip and the common lead together – this should produce a near zero indication.

 

(    )         Adjust the BIAS ADJ control (R-18/20) (on circuit board) for a zero meter indication.

 

(    )         Set the FUNCTION switch to the DC– position.

 

(    )         Adjust the ZERO ADJUST control (R-19) fully clockwise.

 

(    )         Meter should indicate approximately 1.5 on the black 15-volt scale.

 

(    )*       Adjust the ZERO ADJUST control (R-19) counter-clockwise for a zero meter indication.

 

(    )*       Alternate the FUNCTION switch between the DC+ and DC– positions.

 

(    )         Repeat the above two marked steps* until no change in the meter indications.

 

•         This setting of the BIAS ADJ control should allow for future adjustments to zero out the meter as the battery voltage decreases over a period of time.  When this zero cannot be reached by adjusting the ZERO ADJUST control, the BIAS ADJ may be reset without disturbing the calibration.

 

* * * * * * *

FINAL ADJUSTMENTS

 

(    )         Set the POWER switch to the OFF position.

 

(    )         Set the test probe tip selector switch to the DC position.

 

(    )         Unplug the test probe phone plug from the input jack.

 

(    )         Set the FUNCTION switch to the DC+ position.

 

(    )         Set the VOLTS switch to the 150 position.

 

(    )         Calibration procedure is complete.