National Instruments 781986-25 PXI Programmable Resistor Module

The National Instruments 781986-25 (or PXIe 2725) is an 18-channel PXI Programmable Resistor Module. It is engineered for simulating resistance-based inputs and outputs that include potentiometers, resistance temperature detectors (RTDs), voltage dividers, and bridge elements. This module utilizes a series of relays to precisely adjust resistance across each channel that facilitate accurate simulation of environmental conditions in hardware-in-the-loop (HIL) validation. Its software interface accepts inputs in temperature or resistance units.

The 781986-25 offers a maximum voltage of 60 VDC or 30 VACrms (CAT I) between channels and ground along with a maximum current of 0.3 A per channel and a power capacity of 0.25 W per channel. The resistor accuracy stands at 0.5% along with a temperature coefficient of resistance (TCR) at 100 ppm. Each channel operates within a resistance range of 1 Ω to 255 Ω, adjustable in 1 Ω steps. The typical initial DC offset resistance is below 1 Ω, but it may rise to 3 Ω at the end of the relay's life, influenced by relay contact and trace resistances.

Dynamic performance of the NI 781986-25 unit includes the simultaneous drive limit of up to 161 relays with a relay operate/release time of 250 μs. The relay life expectancy is substantial that offers up to 1 × 108 cycles under low power loads (<50 mW) and up to 1 × 106 cycles at full power load (<250 mW). Triggering is facilitated by PXI trigger lines <0...7> with a minimum pulse width of 150 ns. The 781986-25 resistor module features a 37-pin D-SUB connector on the front panel and two 2 × 2 Micro-Fit connectors for DMM ports. It operates on a power requirement of 1.2 W at 3.3 V and a maximum of 11 W at 12 V.

The compact design fits into a single 3U PXIe/cPCI slot and measures 21.6 × 2.0 × 13.0 cm in size. The 781986-25 weighs around 323 g. It is designed for indoor use within a temperature range of 0 °C to 55 °C and storage temperatures from -20 °C to 70 °C. In compliance with various electromagnetic compatibility and safety standards, the NI 781986-25 meets EN 61326-1, EN 55011, AS/NZS CISPR 11, FCC 47 CFR Part 15B, and ICES-001 for emissions. It also aligns with IEC 61010-1, EN 61010-1, UL 61010-1, and CSA 61010-1 for safety.