II. Model Interpretation

PXI: PCI eXtensions for Instrumentation, compatible with PXI/PXIe hybrid slots.

2521: 2500 Series (General Relay Switch), 21 represents 40 channels, DPST double-throw, 150V/2A specification.

Part Number: 778572-21.

Status: In stock (NI mainstream DPST general switch module).

III. Technical Specifications

Channel Configuration

Relay Type: 40 independent DPST (Form A, double-throw normally open) non-latching armature relay.

Topology: 40 fully independent double-throw channels, no matrix / multiplexing structure.

Electrical Characteristics

Maximum switching voltage: 150 VDC (channel-to-channel / channel-to-ground).

Maximum switching current: 2 A (per channel).

On-state resistance: <0.5 Ω (typical).

Thermal offset: Low (suitable for precise differential measurement).

Relay lifespan: 10^7 times (resistive load, typical).

Dynamic Performance

Bandwidth: 25 MHz.

Switching time: <5 ms (typical).

Scan rate: 145 cycles/second.

Physical and Environmental

Size: 3U PXI (100 mm×160 mm).

Weight: Approximately 0.35 kg.

Operating Temperature: 0–55 °C; Storage: −40–70 °C.

Humidity: 10%–90% RH (no condensation).

IV. Interface and Communication Configuration

Host Interface: PXI Hybrid Bus (compatible with PXIe/PXI), supports hot plugging, plug-and-play.

Signal Interface: 160-pin DIN female connector (front panel), each channel includes CHx+/CHx− (signal terminals) and COMx+/COMx− (common terminals), suitable for differential / floating ground wiring.

Trigger and Synchronization: PXI trigger lines (TTL0–TTL4, 70 ns resolution), supports multi-module synchronous scanning and timing control.

Driver Software: Compatible with NI-SWITCH, LabVIEW, TestStand, C/C++/Python API, supports IVI standard driver.

V. Core Functions

40 independent DPST double-throw channels: Each channel is independently controlled for positive/negative dual-line connection, suitable for differential signals, floating ground loads, avoiding common ground interference.

Medium-power double-throw switching: 150 V/2 A double-throw synchronous switching, covering low-voltage differential power supplies, sensors, actuators (heaters, fans, solenoids) control requirements.

Low-resistance low-noise precise switching: <0.5 Ω on-state resistance + low thermal offset, suitable for precise differential voltage / current signal routing and measurement.

Built-in relay count: Built-in relay operation count, facilitating predictive maintenance and early replacement of aging relays.

Software programmable and scanning: Supports immediate control and list scanning, suitable for automated test sequences and real-time control scenarios.

VI. Application Scenarios

Automated Test (ATE): Differential power / signal routing of circuit boards, modules, systems, functional testing and aging testing.

Differential / floating ground signal switching: Dual-line signal switching of sensors, instruments, communication devices, eliminating common ground interference.

Power and load control: Low-voltage differential power distribution, relay / contactor drive, heater / fan / solenoid control.

Industrial control and monitoring: Equipment status monitoring, alarm circuit control, small actuator drive.

Automotive electronic testing: Differential power / I/O interface testing of on-board ECUs, sensors, actuators.

VII. Usage and Maintenance Instructions Installation and Wiring

Module: Disconnect and plug in, insert into the PXI/PXIe hybrid slot, tighten the fixing screws.

Wiring: Connect the 160-pin DIN interface to the differential load / the tested device according to the channel definition. Do not exceed 150 V or 2 A.

Grounding: Connect the chassis to the system ground reliably to reduce electromagnetic interference.

Software Configuration

Install the NI-SWITCH driver, identify the module with NI-MAX, and configure the DPST channel topology.

Programming: Call the switch VI in LabVIEW, or configure the test sequence in TestStand to achieve channel control and scanning.

Daily Maintenance

Cleaning: After power off, wipe the panel with a soft cloth to avoid liquid entering the DIN interface.

Environment: Working temperature 0–55 °C. Avoid dust, moisture, and strong electromagnetic interference.

Protection Mechanism: Avoid overpressure (>150 V), overcurrent (>2 A), inductive loads (without surge suppression), and extend the relay lifespan.

Static Protection: Wear an anti-static wristband when disconnecting and plugging in the module to ensure a good ground connection for the chassis.