PRS-370 IN DMM MODE UNCERTAINTIES

IET Labs Inc., PRS-370 DMM-Mode Uncertainties

The IET Labs PRS-370 Decade Resistor has a very interesting built-in feature to increase its short-term accuracy. 

If you connect your 8.5 Digit DMM to the rear terminal of the PRS-370 Decade Resistor, the PRS-370 will at the touch of a button, adjust the desired resistance to any value from the range 0.1 Ω – 20 MΩ based upon measurements from the DMM.

The PRS-370 works in a loop to; control the DMM, acquire measurements from the DMM and adjust it's internal source resistoance to achieve an output resistance value as close as possible to the nominal value.  The PRS-370 stops this adjustment process when it is able to source a resistance that is as close a possible to the nominal resistance, within the uncertainty of the DMM. 

Once the process is complete, approx 15-60 seconds, the PRS-370 diplays; nominal resistance, difference from nominal and the measurement accuracy of the DMM, and switches the source resistance from the rear terminals to the front terminals of the PRS-370.

This PRS-DMM feature basically turns your PRS-370 into a short-term transfer standard that is able to source resistance to virtually the same uncertainties as your 8.5 Digit DMM.  It transforms the Fluke 8508A or Keysight 3458A, which you already own, from having the ability to measure to also being able to also source resistance. 

See Chapter 4 of the Manual for More Info on this DMM Feature

When used with a Keysight 3458A or Fluke 8508A your PRS-370 can have the following measurement accuracies shown below.

Note the exact accuracy is displayed on the front panel of the PRS-370 after the loop is completed, so you do not have to look at this table after you own the unit.

The numbers provided are the basic measurement accuracy of the 8508A or 3458A in (ppm) from their respective manuals for a 1 year calibration interval of the DMM at a 95% confidence level. 

This does not include short-term stability of PRS-370.  You would need to add ±1 or 2 ppm/<1 minute or  ±4 ppm/10 minutes to the respective numbers.

Using Fluke 8508A

Resistance Setting (Ω) Measurement Accuracy of 8508A in (ppm) does not include short-term stability of PRS-370
1 20
2 21
3 17
4 15
5 14
6 13
7 12
8 12
9 12
10 11
Decade Step  10Ω to 10kΩ Measurement Accuracy of 8508A in (ppm) does not include short-term stability of PRS-370
1 9
2 15
3 13
4 11
5 11
6 10
7 10
8 9
9 9
10 9
Resistance Setting (Ω) Measurement Accuracy of 8508A in (ppm) does not include short-term stability of PRS-370
100,000 9
200,000 19
300,000 15
400,000 14
500,000 13
600,000 12
700,000 11
800,000 11
900,000 11
1,000,000 11
Resistance Setting (Ω) Measurement Accuracy of 8508A in (ppm) does not include short-term stability of PRS-370
1,000,000 11
2,000,000 25
3,000,000 22
4,000,000 20
5,000,000 19
6,000,000 18
7,000,000 18
8,000,000 18
9,000,000 17
10,000,000 17

Using Keysight/Agilent 3458A

Resistance Setting (Ω) Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
1 65
2 40
3 32
4 28
5 25
6 23
7 22
8 21
9 21
10 20
Resistance Setting (Ω) Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
10 20
20 37
30 29
40 25
50 22
60 20
70 19
80 18
90 18
100 17
Decade Step 100 Ω to 10 kΩ Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
1 17
2 13
3 12
4 11
5 11
6 11
7 11
8 11
9 11
10 11
Resistance Setting (Ω) Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
100,000 11
200,000 25
300,000 22
400,000 20
500,000 19
600,000 18
700,000 18
800,000 18
900,000 17
1,000,000 17
Resistance Setting (Ω) Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
1,000,000 11
2,000,000 25
3,000,000 22
4,000,000 20
5,000,000 19
6,000,000 18
7,000,000 18
8,000,000 18
9,000,000 17
10,000,000 17