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 8588A, 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, Fluke 8588A, 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 Fluke 8588A
| Resistance Setting (Ω) | Measurement Accuracy of 8588A in (ppm) does not include short-term stability of PRS-370 |
| 1 | 16 |
| 2 | 17 |
| 3 | 14 |
| 4 | 12 |
| 5 | 12 |
| 6 | 11 |
| 7 | 10 |
| 8 | 10 |
| 9 | 10 |
| 10 | 10 |
| Decade Step 10Ω | Measurement Accuracy of 8588A in (ppm) does not include short-term stability of PRS-370 |
| 1 | 10 |
| 2 | 12 |
| 3 | 11 |
| 4 | 10 |
| 5 | 9 |
| 6 | 9 |
| 7 | 9 |
| 8 | 8 |
| 9 | 8 |
| 10 | 8 |
| Decade Step 100Ω to 10kΩ | Measurement Accuracy of 8588A in (ppm) does not include short-term stability of PRS-370 |
| 1 | 8 |
| 2 | 12 |
| 3 | 11 |
| 4 | 10 |
| 5 | 9 |
| 6 | 9 |
| 7 | 9 |
| 8 | 8 |
| 9 | 8 |
| 10 | 8 |
| Resistance Setting (Ω) | Measurement Accuracy of 8588A in (ppm) does not include short-term stability of PRS-370 |
| 100,000 | 8 |
| 200,000 | 16 |
| 300,000 | 13 |
| 400,000 | 12 |
| 500,000 | 11 |
| 600,000 | 11 |
| 700,000 | 10 |
| 800,000 | 10 |
| 900,000 | 10 |
| 1,000,000 | 10 |
| Resistance Setting (Ω) | Measurement Accuracy of 8588A in (ppm) does not include short-term stability of PRS-370 |
| 1,000,000 | 10 |
| 2,000,000 | 23 |
| 3,000,000 | 20 |
| 4,000,000 | 19 |
| 5,000,000 | 18 |
| 6,000,000 | 18 |
| 7,000,000 | 17 |
| 8,000,000 | 17 |
| 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 |