IET PRS‑370 Self‑Adjusting Programmable Resistance Decade Substituter

The new generation of precision resistance and automatic self-adjusting

The IET PRS-370 is the most advanced model in the IET Labs PRS family and is a direct replacement for both traditional decade resistors and separate resistance standards. With its patented self-adjusting technology, modern controls and exceptional accuracy, the PRS-370 offers a level of performance previously unavailable in programmable or manual resistance cabinets. The instrument is designed for laboratories and production lines that require absolute precision, automation and reliability.

A new standard in accuracy

The IET PRS-370 delivers a basic accuracy of 70 ppm in Source Resistance mode, but it really stands out in its PRS-DMM mode, where the instrument automatically interfaces with a Fluke 8508A, 8588A or Keysight 3458A. In this mode, the PRS-370 controls the DMM, reads back the measured value and then adjusts its own output to an accuracy better than 10 ppm. This makes the PRS-370 a full-fledged 4-wire variable resistor standard, suitable for applications that normally require fixed reference standards.

Automatic self-adjustment without a PC

One of the most impressive features of the PRS-370 is that automatic adjustment takes place entirely within the instrument. No PC or external software is required. The PRS-370 configures the DMM to the correct measurement mode, reads the resistance and corrects its output until the deviation is minimal. The user can immediately see the nominal value, the measured value, the deviation in ppm and the catalogue uncertainty of the DMM on the colour touchscreen. Once the adjustment is complete, the instrument automatically switches to the front connections so that both the DMM and the device under test can be connected simultaneously. The resistance then remains stable for a long period of time, making the PRS‑370 ideal for accurate, short-term reference measurements.

Source Resistance mode for general applications

For applications where no DMM coupling is required, the PRS-370 functions as a highly accurate programmable decade resistor. The user can enter values via the touchscreen or via GPIB control. The PRS-370 features an advanced algorithm that improves accuracy by 30% and increases resolution a thousandfold over traditional decade boxes. The built-in firmware also includes an automatic calibration routine: simply connect a DMM and the instrument will calibrate its internal resistors itself, without manual trimming procedures. The calibration history of each resistor is stored and can be read via GPIB for analysis.

RTD simulation without additional corrections

Like the PRS-330, the PRS-370 supports direct RTD simulation for PT-100 and PT-1000, without the need for tables or corrections. The user enters a temperature in Celsius or Fahrenheit, and the instrument automatically programmes the corresponding resistance. Four custom RTD tables can be stored for specific applications.

Modern controls and connectivity options

The PRS‑370 features a bright colour touchscreen with soft keys, a numeric keypad and a clear interface. Both the front and rear connections are equipped with low-EMF, gold-plated tellurium-copper binding posts, allowing DMM and DUT to be connected simultaneously. For automation, a GPIB interface is provided as standard, with support for SCPI commands and both listener and controller modes. For users who require Ethernet or USB, IET refers to the PRS-330, which includes these interfaces as standard.

Reliability and long service life

The PRS-370 is built with high-quality wirewound and metal foil resistors, combined with relays with an expected service life of 100 million switching cycles. Stability is 50 ppm per year, and thermal EMF remains below 15 µV. Automatic adjustment and the ability to quickly calibrate internal resistors ensure long-term performance and reliability.

The PRS‑370 is a unique combination of programmable resistance, RTD simulator and self-calibrating reference standard. Its accuracy, automation and ease of use make it a powerful solution for laboratories working at the highest level of electrical metrology. The PRS-370 not only replaces traditional decade boxes, but also fixed resistance standards — and does so with a flexibility and precision that is unmatched in this class.