Load Cell Amplifier
What is a Load Cell Amplifier?
Otherwise known as signal conditioning amplifiers or load cell conditioners, these devices take the milli-volt scale differential output from a load cell and convert it into a form suitable for onward transmission to a remote point for display, logging or for use as feedback in a control loop or interlock chain.
A load cell is a transducer which produces a voltage output proportional to applied load.
Load cells contain a number of strain gauge elements bonded to a load bearing structure so that applied load results in a change of resistance across each strain element. This resistance change is extremely small so elements are usually connected as a Wheatstone bridge where the output is in the form of a very low differential voltage. For this reason the input stage of the load cell amplifier is generally some form of instrumentation amplifier converting the differential input into a form suitable for further conditioning.
For load cell calibration a method of setting signal offset and gain is provided so that the output more closely represents the applied load.
Lastly, in the case of an analogue load cell amplifier there is an output stage to convert the signal into a voltage or current output.
In addition to their role as a signal conditioner a load cell amplifier must also provide a stable low voltage dc output used as the excitation supply to the strain bridge.
Selection of bridge resistance is of particular importance if the load cell amplifier is to be battery powered. Battery life may be extended by switching the excitation supply so that it is only applied to the bridge when the bridge output is to be sampled.
Load Cell Amplifier Types
Broadly speaking, the amplifiers fall into one of the two following categories:
Analogue Load Cell Amplifier
Input circuits have to exhibit very low drift and have very good long term stability so some form of instrumentation amplifier is generally employed. Depending on the model, input gain can be set either by switch selection or resistor change to match the transducer sensitivity.
Transducer sensitivity could range from 0.5 to 150mV/V but is typically 2.5mV/V.
Signal conditioning circuits for offset, gain and filtering usually employ operational amplifiers so the circuitry has to be carefully designed for good linearity, low drift and good thermal stability.
Output may be in the form of a uni-polar or bi-polar voltage or a 4 to 20mA current loop which, compared to voltage outputs, has the advantage of improved immunity to electrical noise picked up on the output cabling - noise impressed on current loop cables is added to the signal on one leg and subtracted on the other leg so is to some extent self cancelling.
Depending on the model, calibration and configuration is accomplished by DIP switch, jumpers or potentiometer setting.
Find an analogue load cell amplifier for your application
Mantracourt design and manufacture a range of analogue load cell amplifiers
including miniature embedded formats such as the ICA ‘in cell’ load call
amplifier suitable for OEM applications.
The LCA Weighing Amplifier provides
an extremely versatile indicator / signal amplifier for single or multiple
load cell applications.
Digital Load Cell Amplifier
Input circuit requirements are identical to those for analogue amplifiers but as soon as the signal is digitised drift and stability are no longer a problem from that point on.
Digital signal processing techniques can be applied by use of an embedded processor, in its simplest form this may be limited to offset and gain calculations for calibration but may extend to digital filtering, tare, and peak hold; scaling can be applied so that output values are displayed in specified true engineering units.
Output may be in the form of a local display or any industry standard or bespoke serial communications format.
Where the device is used as a controller, relays can be programmed to change state at predefined threshold crossings. Some models can be fitted with optional output modules to give voltage or current loop outputs.
Configuration may be by DIP switch setting, jumpers, potentiometer setting, local keypad and display or via serial link from a host controller or programming device.
Find a digital load cell amplifier for your application
For USB output, the DSCUSB will provide a load cell input to a digital USB serial output which simply plugs into your PC where our software will configure, calibrate and log load cell data. The DSC packaged in a convenient field terminal enclosure gives high performance and high speed digital signal conditioning, or as an OEM module for embedding into load cells see the DCell. The SMW provides a load cell display and controller with both digital and analogue outputs. Also see our range of digital indicators including the portable load cell indicators.
- DSCUSB
- DSC
- Dcell
- SMW
- See all Digital Output Signal Converters
- Wireless Load Cell Amplifiers are also available as part of Mantracourt’s T24 radio telemetry range which provides the hardware and software to create wireless load cells and other wireless sensors. See a telemetry handheld display.
See Also load cell indicators
