Load cells (force sensors)

ITLL load cell inventory

Bridge-Based Sensors

Pulled straight from NI-DAQmx Help; this is an explanation of how bridge-based load cells work:

Bridge-based sensors operate by correlating a physical phenomena, such as strain, temperature, or force, to a change in resistance in one or more legs of a Wheatstone bridge. The general Wheatstone bridge, shown in the following figure, is a network of four resistive legs with an excitation voltage, V_EX, that is applied across the bridge. One or more of these legs can be active sensing elements.

The Wheatstone bridge is the electrical equivalent of two parallel voltage divider circuits. R1 and R2 compose one voltage divider circuit, and R4 and R3 compose the second voltage divider circuit. You measure the output of a Wheatstone bridge between the middle nodes of the two voltage dividers.

A physical phenomena, such as a temperature shift or a change in strain applied to a specimen, changes the resistance of the sensing elements in the Wheatstone bridge. You can use the Wheatstone bridge configuration to help measure the small variations in resistance that the sensing elements produce corresponding to a physical change in the specimen.

Using an NI-9237 DAQ to read force data

You will need:

load cell
NI breakout (RJ-50 [looks like an ethernet but has 10, not 8 pins] to screw terminal)
RJ-50 cable (see note above about resemblance to ethernet cable)
NI-9237
NI DAQ
Computer with LabVIEW/NI MAX

This is the connection diagram: