DATRON INSTRUMENTS 1061 (01) PDF Document

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What is the purpose of calibrating the DATRON INSTRUMENTS 1061?

The purpose of calibration on the DATRON INSTRUMENTS 1061 is to take account of any long-term drifts in the components of the instrument and to restore the accuracy, traceable to a known standard.

The period between calibrations depends upon the accuracy performance required from the instrument and for guidance, guaranteed accuracies for 24 hours, 90 days and 1 year are quoted.

What are the essential requirements for a good calibration of the DATRON INSTRUMENTS 1061?

To ensure a good calibration for your DATRON INSTRUMENTS 1061, please follow these guidelines:

Temperature: So that the instrument can meet its specification over the quoted temperature range, the temperature environment should be stabilized at 23°C ±1°C. In addition, temperature gradients around the instrument should be considered, therefore calibrate the instrument in its normal operating position and allow plenty of room for ventilation.

Warm up: It is essential that the instrument has fully temperature stabilized if the best results from calibration are to be achieved. Therefore, at least a 2 hour warm up period is recommended during which time the line supply to the unit should not be removed even for a short period. In addition, if the covers have been removed, make certain that they are correctly fitted and that the leaf contacts to the Earth and Guard Shields are in good shape.

Calibration Source: To perform a useful calibration, the accuracy of the source should always be at least four times that of the instrument being calibrated. In most cases, examples of likely sources are given for each calibration function.

Guarding: It is preferable to arrange for the DVM to be ‘calibrated with Local Guard’ selection. Furthermore, to arrange for the ‘Lo’ terminal of the DVM to be ‘earthed’ throughout and let the calibration source float. If a Remote Guard connection is necessary, then examples are shown in the Operating Manual.

How does the ‘AUTOCAL’ process work on the DATRON INSTRUMENTS 1061?

The ‘AUTOCAL’ process on the DATRON INSTRUMENTS 1061 means that complete calibration of all AC, DC, Ohms and Current on every range can be carried out from the instrument’s own front panel. In this process, an internal non-volatile memory stores calibration constants for each function and range as determined when the instrument takes a series of 16 readings of the applied calibration source. Internally, each of the readings is devided by one-sixteenth of a digit and when the average is taken, the instrument is able to resolve to better than one least significant digit displayed.

Access to the non-volatile memory is gained using a key inserted into the rear panel. When calibration is complete, the key is removed, thereby preventing accidental or unauthorized use of the calibration routine.

The five ‘AUTOCAL’ Keys are:

‘Zero’: This takes account of offsets in the instrument and in the calibration source.

‘Gain’: This sets a scaling factor for each range and function.

‘Ib’: This nulls the input bias current of the DC voltage measurement circuitry, to around 10pA. Therefore it only has a significant effect on the low DC voltage ranges and high resistance Ohms ranges. It can be operated as often as required and independently of other calibration operations. It will be seen that successive operations of ‘Ib’ approach the final nulled value of current iteratively.

‘AcHf’: This flattens the response of the A.C. amplifier used for AC voltage measurement. It should only be used when a full calibration i.e. ‘Zero’, ‘Gain’ and ‘AcHf’ is carried out. As with ‘Ib’ the calibration action is iterative and requires several operations of the key to complete.

‘Lin’: This is an important calibration operation as it optimises the basic linearity of the internal measurement circuitry used for all ranges and functions. It must be used before any DC voltage or Ohms calibration is carried out.

How do I perform the ‘AUTOCAL’ procedure on the DATRON INSTRUMENTS 1061?

To perform the ‘AUTOCAL’ procedure on your DATRON INSTRUMENTS 1061, follow these steps:

1. Select the ‘FUNCTION’ and ‘RANGE’ to be calibrated and cancel any ‘MODE’ or ‘COMPUTE’ buttons.

2. Insert the key into the ‘CALIBRATE ENABLE’ keyswitch on the rear panel and turn to the ‘CAL’ position. (The ‘cal’ legend will be displayed on the front panel.)

3. If the instrument is fitted with Option 50 IEEE Bus, set the rear panel address switch to 31 i.e. all 1’s.

4. Connect the calibration source to the input terminals and operate the keys in the tables in the following pages. When a ‘CALIBRATE’ button is operated, its associated L.E.D. indicator will light and extinguish when the calibration operation is executed.

5. When all calibration is complete turn the keyswitch to ‘RUN’ and remove the key.

What does an ‘Error 4’ message during calibration on the DATRON INSTRUMENTS 1061 indicate?

During calibration on the DATRON INSTRUMENTS 1061, if ‘Error 4’ is displayed, this indicates that the calibration source deviates too far from the calibration span of the instrument. Under these circumstances, the calibration memory is not updated and the instrument is put into ‘Hold’ with the calibration button calibaration key LED remains on.

In the case of ‘Zero’, ‘Gain’ or ‘AcHf’ the Calibration Source should be checked and the same ‘CALIBRATE’ key depressed. The ‘Hold’ mode may be released at any time and the instrument will be free-running. If ‘Error 4’ follows ‘Ib’ or ‘Lin’ or persistently appears following ‘Zero’, ‘Gain’ or ‘AcHf’ then an instrument failure may have occurred.

How do I perform a DC Voltage Calibration on the DATRON INSTRUMENTS 1061?

The procedure in the table below is all that is necessary to completely ‘AUTOCAL’ the DC voltage function. Steps 1 and 2 affect the accuracy on all ranges and should therefore be carried out even if just one range is being calibrated.

Step	Calibration Operation	Calibration Source Output	DVM Setting	‘CALIBRATE’ Key	DVM Reading After Calibration	Remarks
1	Linearity	1MΩ Lin Source	DC, 1 Filter[1]	‘Lin’	<10 digits (<100 digits)	This calibration step may take around 30 seconds to complete.
2	Input Bias Current	10MΩ Ib Source	DC, 1	‘Ib’	<100 digits	Each subsequent operation of ‘Ib’ should approximately halve the DVM reading.
3	10V Range Zero	+0.0000V	DC, 10	‘Zero’	±0.0000V
4	10V Positive Full Range	+10.0000V	DC, 10	‘Gain’	+10.0000V
5	10V Range Zero	-0.0000V	DC, 10	‘Zero’	±0.0000V
6	10V Negative Full Range	-10.0000V	DC, 10	‘Gain’	-10.0000V
7	1V Range Zero	+0.00000V	DC, 1	‘Zero’	±0.00000V
8	1V Positive Full Range	+1.00000V	DC, 1	‘Gain’	+1.00000V
9	1V Range Zero	-0.00000V	DC, 1	‘Zero’	±0.00000V
10	1V Negative Full Range	-1.00000V	DC, 1	‘Gain’	-1.00000V
11	.1V Range Zero	±0.000mV	DC, .1	‘Zero’	±0.000mV ±1 digit	Wait for the reading to stabilize before operating ‘Zero’
12	.1V Positive Full Range	+100.000mV	DC, .1	‘Gain’	+100.000mV ±1 digit
13	.1V Range Zero	-0.000mV	DC, .1	‘Zero’	±0.000mV ±1 digit	Wait for the reading to stabilize before operating ‘Zero’
14	.1V Negative Full Range	-100.000mV	DC, .1	‘Gain’	-100.000mV ±1 digit
15	100V Range Zero	+0.000V	DC, 100	‘Zero’	±0.000V
16	100V Positive Full Range	+100.000V	DC, 100	‘Gain’	+100.000V
17	100V Range Zero	-0.000V	DC, 100	‘Zero’	±0.000V
18	100V Negative Full Range	-100.000V	DC, 100	‘Gain’	-100.000V
19	1000V Range Zero	+0.00V	DC, 1000	‘Zero’	±0.00V
20	1000V Positive Full Range	+1000.00V	DC, 1000	‘Gain’	+1000.00V	Lethal voltages present. Increase calibration source in 100V steps if possible.
21	1000V Range Zero	-0.00V	DC, 1000	‘Zero’	±0.00V
22	1000V Negative Full Range	-1000.00V	DC, 1000	‘Gain’	-1000.00V	Lethal voltages present. Increase calibration source in 100V steps if possible.

[1] For 1061A, Input Filter increases resolution by 1 digit – 1061A tolerance given in brackets ( ).

How do I perform an Ohms Calibration on the DATRON INSTRUMENTS 1061?

The procedure in the table below is all that is necessary to completely ‘AUTOCAL’ the Ohms function. If just the Ohms or just one range of the DC Ohms is to be calibrated, then steps 1 and 2 in the DC Voltage Calibration table should be carried out first. Then on each Ohms range just a ‘Zero’ and ‘Gain’ calibration is required.

For accurate ‘Zero’ calibration on Ohms it is ESSENTIAL that a correctly connected zero source is used. Two arrangements are shown in Fig 1.1; it can be seen that 4 wire ‘Ω’ selection is recommended on all ranges.

Step	Calibration Operation	Calibration Source	DVM Setting	‘CALIBRATE’ Key	DVM Reading After Calibration	Remarks
1	10Ω Range Zero	4 wire zero	kΩ, 4 wire, 10Ω	‘Zero’	±0.0000Ω ±1 digit	Wait for the reading to stabilize before operating ‘Zero’
2	10Ω Full Range	10Ω [1] Standard Resistor	kΩ, 4 wire, 10Ω	‘Gain’	10.0000Ω ±1 digit	Wait for the reading to stabilize before operating ‘Gain’
3	.1kΩ Range Zero	4 wire zero	kΩ, 4 wire, .1	‘Zero’	±0.000Ω
4	.1kΩ Full Range	100Ω [1] Standard Resistor	kΩ, 4 wire, .1	‘Gain’	100.000Ω
5	1kΩ Range Zero	4 wire zero	kΩ, 4 wire, 1	‘Zero’	±0.0000kΩ
6	1kΩ Full Range	1kΩ [1] Standard Resistor	kΩ, 4 wire, 1	‘Gain’	1.00000kΩ
7	10kΩ Range Zero	4 wire zero	kΩ, 4 wire, 10	‘Zero’	±0.0000kΩ
8	10kΩ Full Range	10kΩ [1] Standard Resistor	kΩ, 4 wire, 10	‘Gain’	10.0000kΩ
9	100kΩ Range Zero	4 wire zero	kΩ, 4 wire, 100	‘Zero’	±0.000kΩ
10	100kΩ Full Range	100kΩ [1] Standard Resistor	kΩ, 4 wire, 100	‘Gain’	100.000kΩ
11	1000kΩ Range Zero	4 wire zero	kΩ, 4 wire, 1000 Input Filter[2]	‘Zero’	±0.00kΩ (±0.000kΩ)
12	1000kΩ Full Range	1000kΩ [1] Standard Resistor	kΩ, 4 wire, 1000 Input Filter[2]	‘Gain’	1000.00kΩ ±5 digits (1000.000kΩ) (±10 digits)
13	10MΩ Range Zero	4 wire zero	kΩ, 4 wire, 10MΩ Input Filter[2]	‘Zero’	±0.0000MΩ (±0.00000MΩ)
14	10MΩ Full Range	10MΩ [1] Standard Resistor	kΩ, 4 wire, 10MΩ Input Filter[2]	‘Gain’	10.0000MΩ ±5 digits (10.00000MΩ) (±50 digits)

[1] – With Standard Resistor sources it may be useful to use the ‘KEYBOARD’ method of calibration.

[2] – For 1061A, Input Filter increases resolution by 1 digit, so 1061A figures are given in brackets ( ).

How do I perform an AC Voltage Calibration (Option 10) on the DATRON INSTRUMENTS 1061?

The procedure in the table opposite is all that is necessary to completely ‘AUTOCAL’ the AC voltage function. On each range just a ‘Zero’, ‘Gain’ and ‘AcHf’ calibration is required.

Step	Calibration Operation	Calibration Source Output	DVM Setting	‘CALIBRATE’ Key	DVM Reading After Calibration	Remarks
1	DC coupled AC Zero	Copper Shorting link	AC, DC, .1	‘Zero’	0.000mV ±3 digits	Set ‘Local Guard’. Do not set ‘Input filter’. Wait for reading to stabilize before operating ‘Zero’
2	.1V Range Zero	Copper Shorting link	AC, .1	Check only	< 100 digits
3	1V Range Zero	Copper Shorting link	AC, 1	‘Zero’	0.0000V ±1 digit
4	10V Range Zero	Copper Shorting link	AC, 10	‘Zero’	0.0000V ±1 digit
5	100V Range Zero	Copper Shorting link	AC, 100	‘Zero’	0.000V ±1 digit
6	1000V Range Zero	Copper Shorting link	AC, 1000	‘Zero’	0.00V ±1 digit
7	10V Full Range LF	10V rms 500 Hz	AC, 10 Input filter	‘Gain’	10.0000V ±1 digit	Select ‘Input filter’ for remaining steps
8	10V Full Range HF	10V rms 30 kHz	AC, 10 Input filter	‘AcHf’	10.0000V ±5 digits
9	1V Full Range LF	1V rms 500Hz	AC, 1 Input filter	‘Gain’	1.00000V ±1 digit
10	1V Full Range HF	1V rms 30 kHz	AC, 1 Input filter	‘AcHf’	1.00000V ±5 digits
11	.1V Full Range LF	.1V rms 500 Hz	AC, .1 Input filter	‘Gain’	100.000mV ±2 digits
12	.1V Full Range HF	.1V rms 30 kHz	AC, .1 Input filter	‘AcHf’	100.00mV ±5 digits
13	100V Full Range LF	100V rms 500 Hz	AC, 100 Input filter	‘Gain’	100.000V ±1 digit
14	100V Full Range HF	100V rms 30 kHz	AC, 100 Input filter	‘AcHf’	100.000V ±5 digits
15	1000V Full Range LF	1000V rms 500 Hz	AC, 1000 Input filter	‘Gain’	1000.00V ±1 digit	Lethal voltage present. Increase calibration source in 100V steps if possible.
16	1000V Full Range HF	1000V rms 20kHz	AC, 1000 Input filter	‘AcHf’	1000.00V ±5 digits	Lethal voltage present. Increase calibration source in 100V steps if possible. DO NOT EXCEED 25 kHz.

How do I perform a DC Current Calibration on the DATRON INSTRUMENTS 1061?

The procedure in the table below shows all that is necessary to completely ‘AUTOCAL’ the DC Current function. If just the DC Current or just one range of DC Current is to be calibrated, then step 11 or 14 of the DC Voltage Calibration table should be carried out first. Then on each current range just a ‘Zero’ and ‘Gain’ calibration is required.

Step	Calibration Operation	Calibration Source Output	DVM Setting	‘CALIBRATE’ Key	DVM Reading After Calibration	Remarks
1	.1mA Range Zero	0.000µA	DC, I, .1	‘Zero’	±0.000µA	Do not select ‘Input filter’
2	.1mA Full Range	+100.000µA	DC, I, .1	‘Gain’	+100.000µA ±2 digits
3	1mA Range Zero	0.0000mA	DC, I, 1	‘Zero’	±0.0000mA ±1 digit
4	1mA Full Range	+1.00000mA	DC, I, 1	‘Gain’	+1.00000mA ±1 digit
5	10mA Range Zero	0.0000mA	DC, I, 10	‘Zero’	±0.0000mA
6	10mA Full Range	+10.0000mA	DC, I, 10	‘Gain’	+10.0000mA
7	100mA Range Zero	0.000mA	DC, I, 100	‘Zero’	±0.000mA
8	100mA Full Range	+100.000mA	DC, I, 100	‘Gain’	+100.000mA
9	1000mA Range Zero	0.00mA	DC, I, 1000	‘Zero’	±0.00mA
10	1000mA Full Range	+1000.00mA	DC, I, 1000	‘Gain’	+1000.00mA

How do I perform an AC Current Calibration on the DATRON INSTRUMENTS 1061?

The procedure in the table below shows all that is required to completely ‘AUTOCAL’ the AC Current function. If just the AC Current or just one range of AC Current is to be calibrated, then steps 1, 2, 11 & 12 of the Option 10 AC Voltage Calibration table must be carried out first. Then on each range just a ‘Zero’ and ‘Gain’ calibration is required.

Step	Calibration Operation	Calibration Source Output	DVM Setting	‘CALIBRATE’ Key	DVM Reading After Calibration	Remarks
1	DC coupled AC Zero	No connections to DVM input terminals	I, DC, AC, .1	‘Zero’	0.00µA ±5 digits	Do not select ‘Input filter’
2	.1mA Range Zero	“	I, AC, .1	Check only	< ±100 digits	Cancel DC coupled
3	1mA Range Zero	“	I, DC, AC, 1	‘Zero’	0.0000mA ±5 digits
4	10mA Range Zero	“	I, DC, AC, 10	‘Zero’	0.0000mA ±5 digits
5	100mA Range Zero	“	I, DC, AC, 100	‘Zero’	0.000mA ±5 digits
6	1000mA Range Zero	“	I, DC, AC, 1000	‘Zero’	0.00mA ±5 digits
7	.1mA Full Range	100µA, 1 kHz	I, DC, AC, .1	‘Gain’	100.000µA ±10 digits
8	1mA Full Range	1mA, 1 kHz	I, DC, AC, 1	‘Gain’	1.00000mA ±10 digits
9	10mA Full Range	10mA, 1 kHz	I, DC, AC, 10	‘Gain’	10.0000mA ±10 digits
10	100mA Full Range	100mA, 1 kHz	I, DC, AC, 100	‘Gain’	100.000mA ±10 digits
11	1000mA Full Range	1A, 1 kHz	I, DC, AC, 1000	‘Gain’	1000.00mA ±10 digits

How do I use the ‘KEYBOARD’ method for calibration on the DATRON INSTRUMENTS 1061?

The ‘KEYBOARD’ method of calibration on the DATRON INSTRUMENTS 1061 is useful when a calibration source, although set to a nominal value, has known errors. In this situation the known value of the calibration source can be entered into the DVM before the ‘AUTOCAL’ process is executed. The process is functional for a source with a magnitude of between 20% and 120% of the range selected, but it should be noted that an equal magnitude source error at lower percentage end of range produces a higher percentage calibration error. The ‘KEYBOARD’ method operates for both the ‘Gain’ and ‘AcHf’ calibrations.

Example of Calibration using ‘KEYBOARD’

The example shown in the table below uses ‘KEYBOARD’ to calibrate the 1000V AC LF Range Gain at 500V (step 15 of the AC Voltage Calibration table for Option 12).

Step	Calibration Operation	Calibration Source	DMM Setting	‘CALIBRATE’ Key	DMM Reading After Calibration	Remarks
1	1000V Range Zero	1.00V rms 500Hz	AC, 1000	‘Zero’	1.00V ±1 digit
2	Set and Enter Source Value	500.00V rms 500Hz		‘KEYBOARD’ then 5,0,0,·,0,0	0 then +500.00	Lethal voltage present. Increase Calibration Source in 100V steps if possible.
3	1000V AC LF Range Gain Calibration	As above		‘Gain’	500.00V ±1 digit

How do I change the line voltage and frequency settings on the DATRON INSTRUMENTS 1061?

The DATRON INSTRUMENTS 1061 is set to 50Hz, 205V to 255V supplies unless Option 80, 81 or 82 is specified. This information is carried on the instrument identification label located on the rear panel. Alteration to a different line voltage/line frequency may necessitate an instrument recalibration.

Changing Line Voltage:

1. Disconnect power and all signal input/output leads.

2. Locate the link(s) connecting the split primary on the printed circuit board in front of the toroidal line transformer.

3. 115V Operation — Remove LK1 (link 1) and fit LK2 and LK3.

4. 230V Operation — Remove links LK2 and LK3, and fit LK1.

5. Amend instrument identification label.

6. Replace fuse with 160mA anti-surge (230V) or 300mA anti-surge (115V).

7. Replace power fuses with 160mA anti-surge (230V) or 300mA anti-surge (115V).

8. Carry out the Specification Verification tests and recalibrate if necessary.

Changing Line Frequency:

1. Disconnect power and all signal input/output leads.

2. Remove the top cover.

3. 400Hz Operation — Remove link LK5 and fit LK2[1] on the Digital assembly.

4. 50/60Hz Operation — Remove link LK6 and fit LK5[1] on the Digital assembly.

NOTE: This step is only important to ensure a low level of zero drift with variations of temperature. Its response time consuming procedure is carried out initially during manufacture and need only be repeated following replacement of Q12 or any component associated with the temperature compensation circuitry.

5. Amend instrument identification label.

6. Replace the fuse.

7. Carry out the Specification Verification tests and recalibrate if necessary.

How do I replace the battery in the DATRON INSTRUMENTS 1061?

The battery should be replaced on or before the date indicated on the rear panel instrument identification label. To retain the calibration memory, the instrument must be powered on during replacement. Therefore great care must be taken due to voltages up to 260 volts being present inside the instrument.

1. Remove top cover and locate battery on the Digital assembly.

2. Power up instrument.

3. Desolder battery at end of tags and remove from clip. Note that with no battery, positive is terminal to resistor.

4. Replace top cover.

5. Amend instrument identification label (Current date + 5 years).

6. Carry out the Specification Verification tests and recalibrate if necessary.

What is the post-repair adjustment procedure for the Basic DC Instrument on the DATRON INSTRUMENTS 1061?

Follow these procedures after repairs to the Basic DC Instrument of the DATRON INSTRUMENTS 1061.

Power Supplies

1. Turn instrument on and allow 5 minutes warm-up period.

2. Connect DVM Hi to TP8 and Lo to TP28 on the Digital assembly. Adjust R2 on the Rear (Power Supply) pcb assembly to give +5.100V ±25mV.

3. Connect DVM Hi to TP1 and Lo to TP29 on the Analog pcb assembly. Adjust R7 on the Rear (Power Supply) pcb assembly to give +15.000V ±15mV.

4. Connect DVM Hi to TP2 and Lo to TP20 on the Analog pcb assembly. Adjust R12 on the Rear (Power Supply) pcb assembly to give -15.000V ±15mV.

Digital Assembly

5. Switch the instrument off and disconnect the power lead.

6. Isolate the Digital Board by removing the connectors along the centre panel (J1-J5).

7. Connect variable 5V supply and DVM Hi to TP8, Lo to TP28. Reduce supply to 4.950V ±10mV.

8. Set R63 fully clockwise. Connect oscilloscope to TP28 and monitor M53 pin 40. Turn R63 anti-clockwise until TP30 undergoes a high to low transition (or begins to pulse low).

9. Remove variable supply and reconnect items disconnected in steps 5 and 6. Disconnect the oscilloscope. Switch on the instrument.

10. Connect DVM Hi to battery positive terminal, Low to TP28. Check battery voltage is >2.5 volts.

11. Disconnect DVM and connect oscilloscope Hi to TP25, Lo to TP28. Adjust scope trigger until the trace is triggered by the first pulse of each reading burst. Adjust R11 so that the pulses occur every 5ms ±0.5ms.

12. Place instrument into HOLD. Connect oscilloscope Hi to TP7, adjust L2 to give a stable 1.05±0.03V. NOTE: This signal contains about 200mV peak to peak high frequency noise.

Analog Assembly (DC Isolator Section)

16. Centralize R150 and R160.

17. Select 0.1V range DC with FILTER out. Apply a 10MΩ resistor between instrument Hi and Lo. Connect DVM Hi to TL8, Lo to TP20. Adjust FSV R152 with a small trim resistor (50ppm/°C) for a reading of <10mV, using R159 for fine adjustment.

18. Apply a short circuit across the input terminals and adjust R150 for a reading of <50µV at TP13.

19. Connect DVM Hi to TP33 and adjust R160 for a reading of <20µV.

20. Repeat steps 17 to 19 until readings are within specified limits.

21. Re-apply 10MΩ resistor across the input terminals. Note the reading on the front panel display (=A).

22. Solder in R152, with instrument turned off.

Analog Assembly (A-D Converter)

23. Select 100V range and apply short circuit between Hi and Lo. Connect DVM Hi to TP7, Lo to TP20. If reading is +6.42V ±0.03V proceed to step 25.

24. Switch off instrument and make positive reference links B & C, if cut i.e. the links alongside TP7. Switch on instrument and measure voltages on TP7 once more.

25. Connect DVM Hi to TP8. If reading is -6.42V ±0.03V proceed to step 27.

26. Switch off instrument and make negative reference links A to C, if cut i.e. the links alongside TP8. Switch on instrument and measure voltage on TP8 once again.

27. Select HOLD. Connect DVM Hi to TP9. Select correct link value for FSV R11 via R15 to give a reading of 0V±1mV. Solder in resistor.

28. Deselect HOLD and disconnect DVM. Select 1000V range and apply +19mV. Connect oscilloscope Lo to TP21, Hi to TP5. Adjust R20 for noisy waveform at zero point.

29. Remove oscilloscope. Replace covers but do not replace screws. Select 1V DC, filter out and apply 1MΩ across input terminals. Turn rear panel keyswitch to CAL mode and select Lin.

30. Select 1V range and apply 10MΩ across input terminals. Select Ib. Repeat until display reads less than 50 digits.

31. Select 10V range, FILTER and apply short copper link across input terminals. Select ZERO.

32. Apply +10 volts and select GAIN. Repeat until display reads +10.0000 ± ½ digit.

33. Apply +19 volts. If the display reads within the limits +18.9999 to +19.0001, proceed to step 35.

34. Re-apply +10 volts and adjust R23 for a displayed reading of +10 – E. Repeat steps 32-34 until both readings are within the limits indicated.

35. Turn rear panel keyswitch to RUN mode.