NI SCXI-1520

Description

The NI SCXI-1520 is a classic and highly regarded module from National Instruments(now part of Emerson).

Here’s a detailed breakdown of what it is,its key features,and how it’s used.

Overview

The NI SCXI-1520 is an 8-channel,4-wire universal strain gauge and bridge-based input module.It’s designed to be used within National Instruments’SCXI(Signal Conditioning eXtensions for Instrumentation)platform.

In simple terms,it’s not a standalone device.It’s a card that slots into an SCXI chassis(like the SCXI-1000,SCXI-1001,etc.).The chassis provides power,cooling,and a communication bus to connect to a computer,typically via a DAQ card(like a PCI-6251)or a USB/LAN controller.

Key Features and Specifications

•Type:8-channel Strain/Bridge Input Module

•Wiring:Supports 2-wire,3-wire,and 4-wire(true remote sense)quarter-bridge,half-bridge,and full-bridge configurations.The 4-wire capability is a standout feature for high-accuracy measurements as it compensates for lead wire resistance.

•Built-in Excitation:Each channel has its own programmable excitation source,which can be set to 0V,2.5V,5V,or 10V.This is used to power the strain gauge or bridge sensor.

•Sample Rate:Up to 333 kS/s aggregate(when scanned by a compatible DAQ device like an SCXI-1600 series controller).This means it can sample all 8 channels very quickly.

•Hardware Filtering:Includes programmable 4-pole Butterworth anti-aliasing filters for each channel.You can set the cutoff frequency to eliminate high-frequency noise before the signal is digitized.

•Shunt Calibration:Supports built-in shunt calibration on a per-channel basis.This is a critical feature for strain gauge measurements that allows you to simulate a known strain input to verify and calibrate the entire measurement path(sensor,wiring,and module)electronically.

•ADC Resolution:The actual analog-to-digital conversion is handled by the downstream DAQ device(e.g.,an M Series card).The SCXI-1520 conditions the analog signal for that ADC.

Primary Applications

The SCXI-1520 is exclusively used for measuring signals from sensors that change resistance,most commonly:

1.Strain Gauges:The most common use.Measuring stress,strain,force,pressure,torque,and displacement.

2.Load Cells&Force Sensors:Which are essentially precision strain gauges in a Wheatstone bridge configuration.

3.Pressure Transducers:Many use a Wheatstone bridge output.

4.Other Bridge-Based Sensors:Such as certain torque sensors and accelerometers.

How It Works in a System(Typical Setup)

A standard data acquisition system using the SCXI-1520 looks like this:

1.Sensor:e.g.,a strain gauge is glued to the test object.

2.SCXI-1520 Module:The sensor wires connect to the terminal block on the front of this module.

3.SCXI Chassis:The SCXI-1520 module is installed into a slot in the chassis(e.g.,SCXI-1000).

4.DAQ Interface:The chassis is connected to the PC via a cable connected to a DAQ card(like a PCI-6251)in the computer’s PCI slot,or to a modern controller module(like the SCXI-1600 USB Controller)that slots into the chassis itself.

5.Software(NI LabVIEW/NI-DAQmx):You configure the module(excitation voltage,filter settings,bridge type)and read the data in software like NI LabVIEW or Measurement&Automation Explorer(MAX).The software automatically scales the raw voltage readings into engineering units(e.g.,micro-strain,pounds,Newton-meters).

Advantages

•High Channel Count:Conditions 8 channels in a single,compact module.

•Excellent Noise Immunity:The 4-wire sensing and robust hardware filtering make it ideal for electrically noisy industrial environments.

•High Accuracy:Dedicated per-channel excitation and true remote sense provide highly accurate measurements.

•Rugged and Reliable:Designed for industrial and test-stand applications.

Important Considerations

•Legacy Product:The SCXI-1520 is now a legacy product by NI.This means it is no longer manufactured or sold new.However,it is extremely common on the secondary market(eBay,used equipment dealers).

•Software Support:It is still fully supported in NI-DAQmx driver software and modern versions of LabVIEW,ensuring it will work with current systems.

•System Required:You must have an SCXI chassis and a compatible method to connect that chassis to your computer.It is not a USB device.

Summary

The NI SCXI-1520 is a high-performance,8-channel signal conditioning module designed specifically for precision strain and bridge measurements.If you need to accurately measure force,pressure,torque,or stress from multiple sensors,especially in a demanding environment,the SCXI-1520 remains an excellent choice,readily available on the used market.