Heathkit Model IT-2240

Digital LC Bridge

 

Date Calibrated:   _____/_____/_____


Calibration Procedure

 

·         Remove all external components from the front panel terminals.

 

Ancillary Equipment Needed

 

Laboratory Standards or supplied Reference Materials

(See section at end of calibration section)

 

* * * * * * *

INITIAL ADJUSTMENTS


Front Panel

 

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

 

(    )         Set the POWER switch to the ON (in) position.

 

(    )         Set the “C” pushbutton switch to ON (in) position.

 

Circuit Board

Refer to PICTORIAL 5-2

Page 18, Illustration Booklet

 

(    )         Adjust the 20 CAL (R154) control to full counter-clockwise.

 

(    )         Adjust the 200 CAL (R152) control to full counter-clockwise.

 

(    )         Adjust the LO D ZERO (R137) control to the center of rotation.

 

(    )         Adjust the HI D ZERO (R203) control to the center of rotation.

 

(    )         Adjust the D CAL control (R202) to the center of rotation.

 

(    )         Adjust the VALUE CAL (R144) control to full counter-clockwise.

 

(    )         Adjust the 2000 CAL control (R226) to full counter-clockwise.

 

(    )         Adjust the VALUE ZERO control (R243) to the center of rotation.

 

(    )         Adjust the BUFFER ZERO control (R232) to the center of rotation.

 

(    )         Adjust the LEAD NULL control (R1) [display board] to full clockwise.

 

(    )         Jumpers W101 to W104 – all closed.

 

* * * * * * *

FINE ADJUSTMENTS

 

v  Handling the body of the calibration capacitors during the following steps may heat them and cause a temporary value change. Therefore handle them only by their leads and for only the shortest possible time.

 

(    )         Set the RANGE switch (front panel) to the 200 nF position.

 

(    )         Adjust the BUFFER ZERO control (R232) to full clockwise.

 

(    )         Adjust the VALUE ZERO control (R243) until the display shows “00.0”.

 

(    )         Adjust the BUFFER ZERO control (R232) to full counter-clockwise.

 

(    )         Adjust the BUFFER ZERO control (R232) slowly clockwise until the display just changes from “00.1” to “00.0”.

 

(    )         Adjust the BUFFER ZERO control (R232) an additional 30o clockwise.

 

(    )         Install the 150 nF standard (.15 mF) capacitor.

 

(    )  (    )1         Set the RANGE switch the 20 mF position.

 

(    )  (    )2         Adjust the VALUE ZERO control (R243) to display the capacitor value rounded to 2 decimals.

 

(    )  (    )3         Set the RANGE switch the 200 nF position.

 

(    )  (    )4         Adjust the VALUE CAL (R144) control to full counter-clockwise.

 

·         The proper number of jumpers has been cut when the display shows at least 20 counts (disregard decimal point) below the 150 nF standard value.

 

(    )  (    )5         If the value displayed is higher than the 150 nF standard – cut jumper W101.

 

(    )  (    )6         If the value displayed still is higher than the 150 nF standard – cut jumper W102.

 

(    )  (    )7         If the value displayed is higher than the 150 nF standard – cut jumper W103.

 

(    )  (    )8         Adjust the VALUE CAL (R144) control until the display shows the 150 nF standard value.

 

(    )         Repeat the above 8 steps * until no further adjustments are required.

 

(    )         Remove the 150 nF standard capacitor.

 

* * * * * * *

RANGE ADJUSTMENTS

 

(    )         Set the RANGE switch the 20 mF position.

 

(    )         Install the 15 mF standard capacitor (observe polarity).

 

(    )         Adjust the 20 CAL (R154) control until the display shows the 15 mF standard value.

 

(    )         Remove the 15 mF standard capacitor.

 

(    )         Set the RANGE switch the 200 mF position.

 

(    )         Install the 150 mF standard capacitor (observe polarity).

 

(    )         Adjust the 200 CAL (R154) control until the display shows the 150 mF standard value.

 

(    )         Remove the 150 mF standard capacitor.

 

(    )         Set the RANGE switch the 2000 mF position.

 

(    )         Install the 1000 mF standard capacitor (observe polarity).

 

(    )         Adjust the 2000 CAL (R154) control until the display shows the 1000 mF standard value.

 

(    )         Remove the 1000 mF standard capacitor.

 

* * * * * * *

D ZERO ADJUSTMENTS

 

·         The HI D ZERO and LO D ZERO controls have a zero position (the display shows .000) where numbers displayed clockwise from zero are considered positive (+) and numbers displayed counter-clockwise are considered negative (–). All settings must be set clockwise from the zero to be positive values.

 

(    )         Set the RANGE switch to the 200 nF position.

 

(    )         Install the 150 nF standard capacitor.

 

(    )         Adjust the HI D ZERO (R203) control to full clockwise.

 

(    )         Hold the D pushbutton switch [front panel] in the ON position.

 

(    )         Adjust the HI D ZERO (R203) control counter-clockwise until the display shows a positive .002.

               [Do not adjust past the zero point]

 

(    )         Release the D pushbutton switch.

 

(    )         Set the RANGE switch to the 2 mF position.

 

(    )         Adjust the LO D ZERO (R137) control to full clockwise.

 

(    )         Hold the D pushbutton switch in the ON position.

 

(    )         Adjust the LO D ZERO (R137) control counter-clockwise until the display shows a positive .002.

               [Do not adjust past the zero point]

 

(    )  (    )1         Set the RANGE switch to the 200 mF position.

 

(    )  (    )2                  Hold the D pushbutton switch in the ON position.

 

(    )  (    )3         Note the display reading _________   _________.

 

(    )  (    )4         Release the D pushbutton switch.

 

(    )  (    )5                  Hold the D pushbutton switch in the ON position.

 

(    )  (    )6         Set the RANGE switch to the 2 mF position.

 

(    )  (    )7         Readjust the LO D ZERO (R137) control to display the same reading.

                        [Do not adjust through the zero point]

 

(    )  (    )8         Release the D pushbutton switch.

 

(    )  (    )9         Set the RANGE switch to the 200 nF position.

 

(    )  (    )10        Install the Dissipation standard resistor in parallel with the150 nF standard capacitor.

 

(    )  (    )11        Hold the D pushbutton switch in the ON position.

 

(    )  (    )12        Adjust the D CAL control (R202) to display the dissipation standard value within +/- .002.

 

(    )  (    )13        If unable to adjust up to the desired value – cut jumper W104.

 

(    )  (    )14        If unable to adjust down to the desired value – close jumper W104 (if open).

 

(    )  (    )15        Remove the Dissipation standard resistor.

 

(    )         Repeat the above 15 steps * until no further adjustments are required.

 

(    )         Remove the 150 nF standard capacitor.

 

(    )         Set the RANGE switch to the 200 pF position.

 

(    )         Adjust the LEAD NULL control (R1) [display board] to display the lowest number.

 

(    )         Return all calibration reference standards to the calibration package.

 

(    )         Set the POWER switch to the OFF position.

 

·         The inductance L ranges have been calibrated as a result of the capacitance C calibration.

 

(    )         Calibration procedure is complete.


* * * * * * *

LABORATORY STANDARDS PREPARATION

 

150 nF standard – Use any value between 100 nF (.10 mF) and 190 nF (.19 mF) known within 0.1% at 1000 Hz. It must have a dissipation of 0.2% (.002) or less.

 

15 mF standard – Use any value between 10 mF and 19 mF known within 0.1% at 120 Hz. It must have a dissipation of 10% (.10) or less.

 

150 mF standard – Use any value between 100 mF and 190 mF known within 0.1% at 120 Hz. It must have a dissipation of 10% (.10) or less.

 

1000 mF standard – Use any value between 1000 mF and 1900 mF known within 0.1% at 120 Hz. It must have a dissipation of 10% (.10) or less.

 

Dissipation standard – This calibration value results from the parallel connection of a resistor R and the 150 nF standard capacitor C. The approximate value for R is determined from:

 

               R = 120/C     Where R is in kW, and C is in nF (.001 uF).

 

For a 100 nF capacitor, approximately 1200 W is required; and for a 190 nF capacitor, approximately 630 W is required. Once the general value has been determined, measure the resistor’s exact value within 0.1%. Also measure the Digital LC Bridge test frequency on the 200 nF range to within 0.1%. The dissipation number (approximately 1.200) can be calculated from:

 

               D = 1000/(2p x f x R x C)     Where f is in kHz, R in kW, and C is in nF.

 

* * * * * * *

SUPPLIED REFERENCE MAINTENANCE

 

Do not allow these calibration components to be exposed to temperatures outside the range of 60 to 90o F (15 to 32o C). Prolonged storage at high or low temperatures will irreversibly alter their values.

 

Do not mechanically stress the leads of these components. Use needlenose pliers to insert the leads into the LC Bridge input contacts. This will not only minimize heating of parts, but also will minimize stress on the leads.

 

At least annually, but no more than twice a year, perform the following Capacitor Reforming steps. For the 15 mF, and 1000 mF electrolytic capacitors, and to a lesser degree for the 150 nF film capacitor, the application of a forming voltage reduces the tendency of the electro-chemical structure in these parts to degrade and/or drift.

 

* * * * * * *

CAPACITOR REFORMING

Refer to PICTORIAL 5-2

Page 18, Illustration Booklet

 

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

 

(    )         Set the POWER switch to the ON (in) position.

 

(    )         Remove the shorting jumper across the S101 (NORM) pins [rear of circuit board].

 

(    )         Place the shorting jumper across the S102 (CAL) pins.

 

(    )         Loosen the – and the +15 screws on terminal strip TS1 [rear of unit].

 

(    )         Secure the leads of the 150 nF capacitor under the screw heads (observe correct polarity).

 

(    )         Allow the capacitor to “form” for approximately one hour.

 

(    )         Carefully remove the capacitor from the screw terminals.

 

(    )         Loosen the – and the +5 screws on terminal strip TS1 [rear of unit].

 

(    )         Repeat the below three steps * for the 15 mF, 150 mF, and the 1000 mF capacitors.

 

(    )  (    )  (    )1       Secure the leads of the capacitors under these screw heads (observe correct polarity and +5 voltage).

 

(    )  (    )  (    )2       Allow the capacitor to “form” for approximately one hour.

 

(    )  (    )  (    )3       Carefully remove the capacitor from the screw terminals.

 

·         No conditioning of the reference resistor is necessary.

 

(    )         Remove the shorting jumper across the S102 (CAL) pins [rear of circuit board].

 

(    )         Place the shorting jumper across the S101 (NORM) pins.

 

(    )         Tighten all the TS1 screws.

 

·         Allow a 24 hour minimum rest period before using these capacitors for calibration.

 

·         Mark the date the capacitors were conditioned as a reminder.

 

(    )         Set the POWER switch to the OFF (in) position.

 

(    )         Disconnect the line cord to the AC power lines.