EDC (Krohn-nite) MV106 DC Voltage standard review and calibration

Krohn-Hite is a company specialized at precision standards and calibration instruments, present on market since 1949.
MV106 is one of it’s legacy, today’s affordable units for precision DC voltage applications, still available on used markets.

While original design comes back from mid 90’s this standard is still pretty nice addition for any lab.

Here’s MV106J Precision DC Voltage Standard Source spec from manual:

Output Voltage ±10nVdc to ±11Vdc
Stability 1 yr. ±(0.0025% of range +2 µV)
OUTPUT ACCURACY ±(0.003% of setting +0.0005% of range +2µV)
Ripple and noise 10 V Range – 50uV, 100mV – 1uV, 10mV – 0.1uV
OUTPUT CURRENT 50mA into RL >100 kOhm
Warm Up Time 30 seconds (min); 60 minutes (max)
Temperature Cal Calibration 23 ° C ±1 ° C
Temp coefficient Operating Limit ±0.001%/° C
Dimensions 133 H x 432 W x 277 D mm

Stability for unit is declared within 25ppm, output accuracy around 30ppm, and tempco is only 10ppm/°C.

Let’s take a look inside of the unit:

There is plenty of room inside. Precision resistors are mounted directly on decade switches,
power transformer located in opposite side, far from any sensitive components.

Output terminals are high-quality copper binding posts, with remote sensing outputs. By default units comes with shorting bars for local sensing on terminals.

Mainboard have low-voltage power supply, analog parts and reference zener diode.

There is label with zener voltage of selected diode sample. It’s not thermally stabilized, so ambient temperature changes will alter it’s output voltage.

Calibration of unit performed via trimmers on main PCB and trimmer board on first decade switch.

—-

Upon arrival unit was tested against next meters:

DMM #1 Keithley 2001, calibrated in 1993
DMM #2 Agilent 34970A with 34901A card, calibrated 9.AUGUST.2011
  • 2.00023 VDC set on EDC

  • 10.00000 mVDC set on EDC

  • 100.00000 mVDC set on EDC

Check with current source in Keithley 2001 in ohms mode:

0.9626 mA – 1kOhm

87.460 uA – 10kOhm

6.9508 uA – 100kOhm

757.29 nA – 0.1MOhm

4.1929 nA – 1GOhm

—-

Calibration procedure and test results

Redmine ticket

Using Keithley 2001 K7 unit after calibration in January 2014

Room temp: 24.3°C (HEL-700 RTD set to 999.999 ohm on same Keithley unit)
20V Range : ±18ppm + 8 counts (Keithley 2001) + absolute ± 100ppm from Tektronix Cal lab.
10V : ±18ppm + 8 counts (Keithley 2001) + absolute ± 54ppm from Tektronix Cal lab.
2V Range : ±18ppm + 4 counts (Keithley 2001) + absolute ± 13ppm from Tektronix Cal lab.
200mV Range : ±25ppm + 12 counts (Keithley 2001) + absolute ± 2.1ppm from Tektronix Cal lab.

Initial cal

1. Zener voltage 1557 – adjustment R1 to set zener voltage. Must be within 100uV

Temperature Zener voltage Vz Zener current Iz D ppm Meas uncertainty
Label 23 to 25C 6.1698 V 7.5 mA ?
Measured 24.3 C 6.169113 V Not measured -111.3 ±18ppm + 8 counts & absolute ± 100ppm
Adjusted 24.3 C 6.169801 V Not measured 0.16 ±18ppm + 8 counts & absolute ± 100ppm

2. Adjust R2 for zero offset, all decades set to zero, DVM on output terminals (local sense)

Measured Vos 24.3 C -0.01629 mV
Adjusted 24.3 C -0.00203 mV

2A. Adjust R2a for sense “0” offset. Set all decades to zero, polarity to plus, range 10V.
Remove sense link from Black (LO) terminals and measure black terminals. Adjust to be less than 1 mV

Measured Vszo 24.3 C 0.81512 mV
Adjusted 24.3 C -0.00101 mV

3. Adjust R3 to set feedback current accurately as required for accurate Vout

Dial 1V on second decade, using 10 position. DVM on output terminals, output read as 1.0000 +- 50uV

Measured Voi 24.3 C 0.9998574 -142.6 ppm
Adjusted 24.3 C 1.0000004 V 0.4 ppm

4. Linearity adjustment of 1st decade

Set setting same as step 3. Set 2nd decade to zero.

5. Set 2V on 1st decade. Adjust P2 pot to output. Set 1V on 1st decade, adjust P1 to 1V.
Vc – after initial cal settings done.

Measured 2V 24.3 C 1.9997686 -115,7 ppm
Measured 2Vc 24.5 C 2.0000546 27,3 ppm
Adjusted 24.5 C 1.9999995 0,3 ppm
Measured 1V 24.5 C 0.9998835 -116,5 ppm
Measured 1Vc 24.5 C 1.0000144 14,4 ppm
Adjusted 24.5 C 1.0000001 0,1 ppm

6. Set 4V on 1st decade to adjust P4. Set 3V to tweak P4.

Measured 4V 24.5 C 3.999532 -117 ppm
Measured 4Vc 24.5 C 4.000046 11,5 ppm
Adjusted 24.5 C 4.000003 0,75 ppm
Measured 3V 24.5 C 2.999645 -118.3 ppm
Measured 3Vc 24.5 C 3.000038 12.7 ppm
Adjusted 24.5 C 2.999994 -2 ppm

7. Set 6V on 1st decade to adjust P6. Set 5V to tweak P6.

Measured 6V 24.4 C 5.999280 -120 ppm
Measured 6Vc 24.5 C 6.000030 5 ppm
Adjusted 24.4 C 6.000007 1,2 ppm
Measured 5V 24.4 C 4.999398 -120 ppm
Measured 5Vc 24.5 C 5.000027 5,4 ppm
Adjusted 24.4 C 5.000003 0,6 ppm

8. Set 8V on 1st decade to adjust P8. Set 7V to tweak P8.

Measured 8V 24.4 C 7.999022 -122,3 ppm
Measured 8Vc 24.5 C 8.000021 2,6 ppm
Adjusted 24.4 C 8.000002 0,3 ppm
Measured 7V 24.4 C 6.999138 -123,1 ppm
Measured 7Vc 24.5 C 7.000018 2,5 ppm
Adjusted 24.4 C 7.000001 0,2 ppm

9. Set 10V on 1st decade to adjust P10. Set 9V to tweak P10.

Measured 10V 24.4 C 9.998775 -122,5 ppm
Measured 10Vc 24.6 C 10.000050 5 ppm
Adjusted 24.6 C 10.000002 0,2 ppm
Measured 9V 24.4 C 8.998888 -123,5 ppm
Measured 9Vc 24.6 C 9.000053 5,9 ppm
Adjusted 24.6 C 9.000001 0,1 ppm

Range set to 100mV

Set setting same as step 3. Set decades to zero.

5. Set 20mV on 1st decade. Adjust P4 pot to output.

Measured 20mV 24.4 C 19.99800 -100 ppm
Measured 20mVc 24.7 C 19.99994 -3 ppm
Adjusted 24.7 C 19.99998 -1 ppm

6. Set 40mV on 1st decade to check

Measured 40mV 24.4 C 39.99562
Adjusted 24.7 C 39.99952

7. Set 60mV on 1st decade to check

Measured 60mV 24.4 C 59.99295
Adjusted 24.7 C 59.99938

8. Set 80mV on 1st decade to check

Measured 80mV 24.4 C 79.99011
Adjusted 24.7 C 79.99916

9. Set 100mV on 1st decade to check

Measured 100mV 24.4 C 99.98775 -122,5 ppm
Adjusted 24.7 C 99.99878 -12,2 ppm

Range set to 10mV

5. Set 2mV on 1st decade.

Measured 2mV 24.4 C 1.99891 -545 ppm
Adjusted 24.7 C 1.99926 -370 ppm

6. Set 4mV on 1st decade to check

Measured 4mV 24.4 C 3.99777
Adjusted 24.7 C 3.99837

7. Set 6mV on 1st decade to check

Measured 6mV 24.4 C 5.99670
Adjusted 24.7 C 5.99758

8. Set 8mV on 1st decade to check

Measured 8mV 24.4 C 7.99581
Adjusted 24.7 C 7.99631

9. Set 10mV on 1st decade to check

Measured 10mV 24.4 C 9.99467 -533 ppm
Adjusted 24.7 C 9.99544 -456 ppm

Measured means before calibration
Adjusted – after calibration

Second calibration procedure and test results

This time recalibration done to much higher standard, calibrated HP 3458A which got DCV transferred from tested LTZ1000A module.

Room temp: +23.5 °C (BME280 reading on RPI)
RH: 66%
Pressure: 1024.4 hPA
3458A TEMP?: 34.3 °C

Initial cal

1. Zener voltage 1557 – adjustment R1 to set zener voltage. Must be within 100uV

Temperature Zener voltage Vz Zener current Iz D ppm Meas uncertainty
Label 23 to 25C 6.1698 V 7.5 mA ?
Measured 23.5 C 6.1696805 V Not measured -19.58 ±6ppm
Adjusted 23.5 C 6.1698013 V Not measured 0.21 ±6ppm

2. Adjust R2 for zero offset, all decades set to zero, DVM on output terminals (4W sense)

Measured Vos 23.5 C -0.00557 mV
Adjusted 23.5 C +0.00005 mV

2A. Adjust R2a for sense “0” offset. Set all decades to zero, polarity to plus, range 10V.
Remove sense link from Black (LO) terminals and measure black terminals. Adjust to be less than 1 mV

Measured Vszo 23.5 C 0.81512 mV
Adjusted 23.5 C -0.00392 mV

3. Adjust R3 to set feedback current accurately as required for accurate Vout

Dial 1V on second decade, using 10 position. DVM on output terminals, output read as 1.0000 +- 50uV

Adjusted 23.5 C 1.00000011 V 0.11 ppm

4. Linearity adjustment of 1st decade

Set setting same as step 3. Set 2nd decade to zero.

5. Set 2V on 1st decade. Adjust P2 pot to output. Set 1V on 1st decade, adjust P1 to 1V.
Vc – after initial cal settings done.

Adjusted 23.5 C 2.0000002 0.1 ppm
Adjusted 23.5 C 1.00000018 0.18 ppm

6. Set 4V on 1st decade to adjust P4. Set 3V to tweak P4.

Adjusted 23.5 C 4.0000005 0.125 ppm
Adjusted 23.5 C 3.0000006 0.2 ppm

7. Set 6V on 1st decade to adjust P6. Set 5V to tweak P6.

Adjusted 23.4 C 6.0000001 0.02 ppm
Adjusted 23.4 C 5.0000006 0.12 ppm

8. Set 8V on 1st decade to adjust P8. Set 7V to tweak P8.

Adjusted 23.5 C 8.0000006 0.08 ppm
Adjusted 23.5 C 7.0000008 0.12 ppm

9. Set 10V on 1st decade to adjust P10. Set 9V to tweak P10.

Adjusted 23.5 C 10.0000005 0.05 ppm
Adjusted 23.5 C 9.0000001 0.01 ppm

Range set to 100mV

Set setting same as step 3. Set decades to zero.

5. Set 20mV on 1st decade. Adjust P4 pot to output.

Adjusted 23.5 C 20.00013 6.5 ppm
Adjusted 23.5 C 39.99980 -5.0 ppm
Adjusted 23.5 C 60.00001 0.17 ppm
Adjusted 23.5 C 80.00012 1.5 ppm
Adjusted 23.5 C 100.00021 2.1 ppm

Range set to 10mV. Meter was nulled at 0V setting.

5. Set 2mV on 1st decade.

Adjusted 23.5 C 1.99921 -395 ppm
Adjusted 23.5 C 3.99846 -385 ppm
Adjusted 23.5 C 5.99765 -391 ppm
Adjusted 23.5 C 7.99680 -400 ppm
Adjusted 23.5 C 9.99596 -404 ppm

Measured means before calibration
Adjusted – after calibration

Repair

One of decade switches was not completely fixed to chassis, which caused rotary switch to turn during operation. After some time one of wires going to rotary switch eventually failed and broke off.

This caused overload lamp to lit, and standard output went to 13.2VDC or -13.2 if negative polarity was selected. Range switch was also changing output range, but none of decades were affecting output voltage.

After soldering wire back, unit come back to normal operation.

Just a reminder to fellow users, ensure all mechanical switches are always firmly seated and fixed.

Author:
Published: Oct. 31, 2014, 3:39 p.m.
Modified: Oct. 23, 2016, 10:57 p.m.

Comments