Choosing the correct load cell amplifier / transmitter may seem like an easy task. As more and more load cell instruments are added to the market every year and with new features it’s best to talk to a load cell electronics sales technician before choosing. Picking the wrong load cell amp can cost extra time and money during the setup and calibration of your scale system.
The load cell amplifier typically refers to an analog output device that changes the small millivolt signal coming from your load cell(s), to a more useful range such as 0-10V or 4-20m. Often times this signal is relayed to a PLC or data acquisition system.
The amp below is a bare bones easily setup device, with analog output that is easy to calibrate. Simply unload the scale set the zero trim pot to output 4mA, apply the load and adjust the mA output to the desired value. The downfall to this type of amp is the zero and span trimpots can affect each others outputs. Sometimes you have to repeat the calibration process several times until you get the output as desired. This is not really an issue unless you are weighing something like a tank when you can’t easily and quickly put test weights on and off the scale.
Load cell transmitter often refers to a device that converts the load cell signal into a digital output, useful in more advanced weighing applications. It is common that load cell transmitters also have an analog output option as well as digital communications. They are typically setup digitally (no fussy trimpots) and have display screens to aid in calibration and troubleshooting the scale. Some models have relay control (via user selectable setpoint values) which could control a checkweighing, bulk filling or unloading application. One of the best features some of these units offer is the ability to perform a theoretical calibration. This can be achieved by entering the load cell(s) full scale mV/V value that is listed on the load cell’s calibration certificate. This is especially useful for high capacity load cells or vessel weighing applications when it is not possible to load the system with known weights.
Common load cell transmitter outputs:
- RS232 / RS485
- Analog 0-10VDC or 4-20mA
- Profibus DP
- Ethernet TCP/IP viewable by internet web browser on local network and worldwide web
- Ethernet IP
- Profinet IO
- PROFINET IO
- SERCOS III
Load Cell Amplifier Selection Conclusion:
We’d recommend going with a digitally calibrated load cell transmitter even if you only require an analog output. The extra $100 in the initial purchase price is easily accounted for when it saves you time during the installation and calibration process. Another advantage is the ability to have a display that shows either the mV input along with analog output values, or some models will display a calibrated weight value of the scale. Making these models much easier to troubleshoot when the time comes.