Load Cell | Force Sensor | Force Measurement Transducer

Understanding how to optimize your output

What are load cell amplifiers?

In real-world applications, load cells (as well as other kinds of sensors/transducers) are often exposed to conditions and environments that may induce signal noise. Furthermore, the output signal of the Wheatstone bridge of most strain-gauge based sensors is is a low-strength signal in mV/V that may not work with other components of your system. A load cell amplifier (or signal conditioner) solves this problem by functioning as a strain gauge reader (i.e. load cell reader) and providing excitation voltage, noise filtering or attenuation, and signal amplification. Hence, it manipulates the sensor's analog signal into a clearer and stronger output that it then converts into easy-to-read, compatible data for systems like PLC, data acquisition modules (DAQ), computers, or microprocessors.

How does an amplifier work?

Excitation Voltage

Full-bridge load cells require an excitation voltage from the Wheatstone bridge amplifier to feed the strain gauge bridge and generate its output signal as a ratio of the input excitation voltage. Thus, you need to establish if your DAQ or PLC can support the sensor’s input voltage or excitation voltage requirements. If you need a load cell amplifier for PLC or DAQ and they do not provide a stable input excitation voltage, the amplifier will be the excitation voltage source to ensure that the sensor provides a reliable and consistent output signal. For example, FUTEK’s USB Load Cell Data Acquisition System can provide excitation for amplified sensors up to 24VDC.

IAA105 Digitally Configurable Analog Voltage Amplifier

Filtering

Analog sensor signals are susceptible to electrical noise and/or residual ripple voltage, which can distort or skew measurements. Noise needs to be filtered out before you can capture an accurate signal. DAQs and PLCs designed to interface directly with full-bridge sensors will include pass band and other forms of signal conditioning and filtration. In a low noise load cell signal conditioner, electronic filters increase accuracy by removing electrical noise and ripple effect above and below the analog sensor’s signal range, resulting in a low signal-to-noise ratio. For example, FUTEK IAA series analog signal conditioners have bandwidth selection features that are used to set the bandwidth from 100 Hz to 50,000 Hz, allowing for noise filtering according to the load cell application.

Amplification

A full-bridge strain gauge sensor can output a signal in the nanovolt through millivolt range. When your DAQ or PLC is limited to measuring volts, you will need a strain gauge amplifier to convert millivolts to a larger signal. Some PLCs and DAQs come with built-in amplification; others will require an external amplifier. For multi-axis sensors, such as a 6 DoF Force Torque sensor, you need a multi-channel load cell amplifier circuit that is able to process all the mV/V outputs of the channels.

USB225 High Resolution & Speed Output Kit

Signal conversion

The majority full-bridge load cells and force measurement sensors (or transducers) generate an analog output in the millivolt range (mV/V). Thus, signal processing is traditionally analog. So, if your PLC or DAQ system requires an amplified analog (i.e.: 4-20 mA, 0-10 VDC) or a digital output (USB, SPI, UART), the load cell needs a strain gauge signal conditioner to convert the mV/V signal to the required signal output. Normally, a load cell display or a load cell indicator is required for local indication (load cell readout) of the force measurement value.

Some applications require digital output, which will require a signal conditioner with an analog-to-digital converter (ADC). For those applications, two critical parameters must be taken into consideration when selecting the digital amplifier: noise-free resolution and sampling rate. In that regards, FUTEK has a broad range of load cell USB output kits

Just as we discussed how important it is to select the right load cell for your application, it is equally important to install your load cell/ force sensor correctly. Most sensor damage and failure occur during setup. It is also critical to install your sensor correctly to get high-quality, accurate readings. It also guarantees ease of use and safe operations.

Avoiding damage - some general guidelines

Do not pull on or carry the sensor by its cable to avoid tension and properly secure the sensor cable to limit cable movement influence.
Avoid bending the strain relief. Bends in the cable should not exceed a radius of ten times the diameter of the sensor cable for dynamic, or moving, applications and not exceed a onetime static, permanent, bend of two to three times the diameter of the cable
Always have the sensor plugged in during installation and handling. This will allow you to monitor the sensor output for effects on zero output during the installation to avoid damage such as permanent zero shift and overload.
Install the sensor in a dry, clean environment, unless the IP rating (see below paragraph) allows for other environments. Many of FUTEK’s sensors have seam-welded stainless steel flexures that provide excellent strength and corrosion resistance as well as enhanced protection against physical damage.
Avoid overloading. Load cells/ force sensors can be accidentally overloaded when improperly handled during installation, which is a very common cause of sensor failure. In order to avoid overloading it’s important to know the limit of the load cell’s load range and not exceed it. Some of FUTEK’s load cells feature built-in 10x overload protection. This prevents sensor damage from direct inline overloads that could occur during the setup process or the occasional system over-range. You also need to ensure that you don’t exceed the sensor’s tolerance for extraneous load conditions. To learn more about how to calculate extraneous load see our comprehensive guide.

IP- ratings and environmental protection

Load cells vary in robustness when it comes to handling environmental factors. IP ratings (also known as an Ingress Protection Rating or International Protection Rating) is a grading system that indicates how well a unit is protected against foreign bodies such as dust, moisture, liquids, and accidental contact. FUTEK offers load cells with an IP-rating of 67, which means the unit can withstand submersion in one meter of water for up to 30 minutes. This limits the risk of damage during installation and opens up more options for applications in wet, rainy, or highly humid conditions.