Understanding Strain Gauge, Hydraulic and Other Load Cell Outputs: How to Choose the Right Signal for Your Project

Load cells are a critical tool for many Western Australian projects, measuring the loads, stresses and forces that impact man made and natural structures.

Whilst strain gauge, hydraulic and other load cells may all measure the same thing, how they output that information can vary. Selecting the right signal format is essential in securing accurate and reliable data.

In this article, we break down the four main load cell outputs and how they could (or couldn’t) work on your site. For more information, contact Monitel.

1. Millivolt (mV/V) Output

This is the most common signal output for strain gauge load cells. It’s a low level, analogue option proportional to the excitation voltage applied (usually around 2 mV/V).

Pros

• Incredibly sensitive and accurate

• Works with most typical data acquisition systems

• Perfect for short cable runs and laboratory work

Cons

• The low voltage signal is prone to electrical interference

• A stable excitation voltage is essential

• Requires significant amplification for success over long cable lengths

How we use it

Monitel consultants opt for a millivolt signal when the logger/unit is located near to the load cell.

2. 4–20 mA Current Loop

In many industries, this is the standard. Instead of voltage, the load cell transmits a current proportional to the load applied. The current sits in the 4 to 20 mA range.

It’s a popular choice for remote field monitoring where sites may be hazardous or hard to access.

Pros

• Great stability over long distances

• Largely immune to voltage drops and electrical interference

• Easy to integrate with remote monitoring systems

Cons

• More costly than most other options

• Signal represents an averaged, less specific force

How we use it

Most WA mining projects are in harsh, remote environments, so our consultants often use this current when monitoring tailings dams and bridge foundations.

3. Vibrating Wire (VW) Frequency

Many load cells use vibrating wire technology that converts force into a frequency. That frequency corresponds to a wire tension altered by the applied load.

• Excellent long term stability

• Highly resistant to harsh climates

• Compatible with long cable runs and geotechnical deployments

Cons

• Only compatible with specialised VW readouts or loggers

• More expensive than a standard strain gauge model

How we use it

In geotechnical settings, long term accuracy is often more important than frequent samples. That’s why our consultants utilise this signal in embankments, tunnels and dams.

4. Digital Outputs (RS-485, Modbus and more)

Digital outputs convert an analogue signal and transmit it via protocols such as RS-485 and Modbus. They are most common in factory settings but are beginning to emerge as a popular choice in field monitoring.

Pros

• Immune to analogue noise

• Easily networked for multi point systems

• Integrates seamlessly with modern loggers

• Precise, complex configuration process

How we use it

Monitel deploys this signal in complex, multi parameter monitoring solutions where load data is networked with other instrumentation.

Geosense and Soil Instruments Output Options

Monitel is proud of our brand and product agnostic approach – we have no allegiance to any one sensor or company. Nonetheless, many of the load cells we use are supplied by Geosense or Soil Instruments. Their configurations include:

• Geosense: Offers strain gauge load cells with mV/V, 4–20 mA, or VW outputs

• Soil Instruments: Well respected for their VW systems with integrated readout options

How Monitel Helps You Find a Signal Output

Our team understands that a one-size-fits-all approach doesn’t work for WA operators.

Whether you’re in the South West or the Pilbara, we’ll assess site conditions, distance to logging equipment, monitoring objectives and regulatory demands to determine the best load cell type and output format. Other considerations include:

• Environmental noise: Electrically noisy sites are best suited to current or frequency outputs.

• Existing systems: We’ll ensure new technology is compatible with your existing dataloggers, telemetry or SCADA.

• Sampling frequency: More dynamic sites may require voltage or digital outputs.

• Project duration: If you’re monitoring long term, we’ll look to stable, low drift technologies like vibrating wire.

Get in Touch and Discuss a Monitoring Solution for Your Site

If you’re unsure which output is best for your load cell monitoring system, our consultants can help you find an ideal solution.

For more information about the price and availability of strain gauge and other load cells, contact Monitel today.