A load cell is an electronic sensor that converts force or weight into an electrical signal. It is a critical component in many industrial and scientific applications, including weighing scales, force testing machines, and material testing equipment. A 3 wire load cell is a particular type of load cell that has three wires – red, white, and black – for electrical connections. In this article, we will discuss the wiring diagram for a 3 wire load cell, how to connect it to a measurement instrument, and some frequently asked questions about load cells.
Wiring Diagram for 3 Wire Load Cell
The wiring diagram for a 3 wire load cell is relatively simple. The three wires are used for the following purposes:
| Wire Color | Purpose |
|---|---|
| Red | Excitation (+) |
| White | Signal (+) |
| Black | Signal (-) |
The excitation wire provides a constant voltage to the load cell, typically between 5-15V DC. The signal wires carry a small electrical signal proportional to the weight or force being measured. The black wire acts as the ground or reference wire for the signal.
To connect a 3 wire load cell to a measurement instrument, you should follow the manufacturer’s instructions carefully. Typically, you will need to connect the excitation wire to a power source, the signal wires to the input channels on the measuring instrument, and the ground wire to the instrument’s ground terminal.
Step-by-Step Guide for Wiring a 3 Wire Load Cell
Here is a step-by-step guide for wiring a 3 wire load cell:
- Identify the wires on the load cell. The red wire is usually the excitation wire, the white wire is the positive signal wire, and the black wire is the negative signal wire.
- Connect the red wire to a stable power source, such as a battery or power supply. The voltage should be within the range specified by the load cell manufacturer.
- Connect the white and black wires to the input channels on the measuring instrument. The load cell signal is usually in the millivolt range, so you should use a high-precision amplifier or signal conditioner to amplify and filter the signal.
- Connect the black wire to the instrument’s ground terminal. This ensures that the signal is referenced to the same ground potential as the measuring instrument.
- Test the load cell and instrument for proper operation. Apply a known weight or force to the load cell and verify that the instrument displays the correct value.
FAQs about Load Cells
1. What is the difference between a 3 wire load cell and a 4 wire load cell?
A 3 wire load cell has three electrical connections – excitation, positive signal, and negative signal. A 4 wire load cell has an additional wire for the ground connection, which is separate from the signal wires. The advantage of a 4 wire load cell is that it eliminates the effects of lead resistance, which can cause errors in the measurement. However, 3 wire load cells are simpler and less expensive to use.
2. How do I choose the right load cell for my application?
The choice of load cell depends on several factors, including the maximum weight or force to be measured, the accuracy required, the environment conditions, and the type of measurement instrument to be used. It is important to consult the load cell manufacturer’s specifications and application notes to ensure that you select the right load cell for your needs.
3. How do I calibrate a load cell?
Load cells require calibration to ensure that they provide accurate and repeatable measurements. Calibration involves applying known weights or forces to the load cell and recording the output signal. You should perform calibration at regular intervals or whenever there is a change in the measurement environment or conditions. Calibration should be carried out according to the manufacturer’s instructions and using appropriate calibration weights or force standards.
4. What are some common problems with load cells?
Common problems with load cells include drift, hysteresis, nonlinearity, and temperature sensitivity. Drift is the gradual change in output signal over time, while hysteresis is the difference in output signal for the same weight or force applied in different directions. Nonlinearity is the deviation from a straight line relationship between applied force/weight and output signal, while temperature sensitivity refers to the change in output signal due to temperature changes. These problems can be minimized by proper selection, installation, and calibration of the load cell and measurement instrument.
5. Can load cells be used in harsh environments?
Load cells can be used in harsh environments, but they may require additional protection or sealing against moisture, dust, and vibrations. There are also load cells specifically designed for use in hazardous or explosive environments, which comply with industry standards such as ATEX or FM.
