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
120
221
317
415
514
613
712
812
912
1011
Decade Step 10Ω to 10kΩMeasurement Accuracy of 8508A in (ppm) does not include short-term stability of PRS-370
19
215
313
411
511
610
710
89
99
109
Resistance Setting (Ω)Measurement Accuracy of 8508A in (ppm) does not include short-term stability of PRS-370
100,0009
200,00019
300,00015
400,00014
500,00013
600,00012
700,00011
800,00011
900,00011
1,000,00011
Resistance Setting (Ω)Measurement Accuracy of 8508A in (ppm) does not include short-term stability of PRS-370
1,000,00011
2,000,00025
3,000,00022
4,000,00020
5,000,00019
6,000,00018
7,000,00018
8,000,00018
9,000,00017
10,000,00017

Using Keysight/Agilent 3458A

Resistance Setting (Ω)Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
165
240
332
428
525
623
722
821
921
1020
Resistance Setting (Ω)Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
1020
2037
3029
4025
5022
6020
7019
8018
9018
10017
Decade Step 100 Ω to 10 kΩMeasurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
117
213
312
411
511
611
711
811
911
1011
Resistance Setting (Ω)Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
100,00011
200,00025
300,00022
400,00020
500,00019
600,00018
700,00018
800,00018
900,00017
1,000,00017
Resistance Setting (Ω)Measurement Accuracy of 3458A in ppm does not include short-term stability of PRS-370
1,000,00011
2,000,00025
3,000,00022
4,000,00020
5,000,00019
6,000,00018
7,000,00018
8,000,00018
9,000,00017
10,000,00017