Several companies manufacture high-quality resistance bridges for both AC and DC applications. All of these bridges can take measurements at the 0.1 ppm level, and research has shown that all of them compensate well for any theoretical inaccuracies predicted in their design.
We like the MI bridge because we feel confident about its measurements, and its software gives us more information than we can get from the other instruments. While it’s true we do use the other bridges for certain functions we undertake in our lab, including some experimental testing, we use the MI bridge every day for fixed-point calibrations of SPRTs.
The 5581 Bridge performs a true auto-balancing procedure to nine significant digits. As the check proceeds, the bridge steps through an internal comparison of the transformer’s windings, the results of which are recorded to track its performance over time.
Another function of this bridge is its real-time uncertainty analysis program. In this mode you enter external uncertainty factors such as the uncertainty of your resistor, and the 5581 combines your information with its own uncertainties to compute a system uncertainty for your measurement.
The optional Windows-control software offers history logging and regression analysis along with uncertainty analysis and the auto-self-check feature. The program also calculates standard deviations if you need them. You can enter coefficients for your SPRT and read temperature rather than resistance.
Of course, if you prefer, you can operate the bridge manually. The choice is yours, but either way you’ll find this to be a great bridge to use.
–0.001W to 0.01W: < 5 ppm 0.01W to 0.1W: < 0.5 ppm 0.1W to 1W: < 0.1 ppm 0.1W to 10 KW: < 0.1 ppm 10 KW to 10 KW: < 0.2 ppm
10 mA to 150 mA, 30-Volt compliance
Automatic 4 to 1000 seconds
100, 120, 220, and 240 V (±10%), 47–63 Hz, 180 VA
60 lb. (27.3 kg)
17" W x 11" H x 15" D (432 x 279 x 381 mm)
< 500 nanovolts
< 20 nanovolts
Relay 2-coil latching
Max Carrying Current
2 A (AC/DC) (optional 30 A)
Inputs and Outputs
Tellurium Copper (rear panel)
5313-001: 40 lb. (18 kg) 5313-002: 20 lb. (9 kg)
5313-001: 17" W x 11" H x 15" D (432 x 279 x 381 mm) 5313-002: 5" H (127 mm)