# How much power does a strain gauge use?

Is it essentially nothing given how small they are? I see most configurations are given 5V, but does that mean they draw amperage as well?

• Just a word of caution - If you've ever attempted to zero or use a bridge ckt that is suffering from thermal drift resulting from strain gauge self-heating due to excessive bridge excitation voltage, you'll never use the full rated value of excitation voltage again. I cringe when I hear people say, "the bridge is rated for a 20V supply." As a rule of thumb, I use 50% of the rated excitation voltage on all strain gauges, load cells, pressure sensors and any other resistance/bridge sensors. Jul 29, 2020 at 19:29

Strain gauges change their resistance depending on the strain they're subjected to. This means that their current draw will vary depending on the strain. The actual resistance of the gauges will be found on the datasheet, but can vary a lot between different products. For example, this one is 120 ohms, and this one is 10 kohms - clearly a big difference. The overall current depends on your configuration: for example, you could use a Wheatstone bridge or a simple potential divider.

As said by the others, they are resistors, so they will consume power depending on how much current runs through them.

That said, if you do not need continuous measurement, you can only activate the measurement current/voltage when you need it.

For example, if you make a battery-powered scale that wakes up when the user stands on it, you would keep the whole circuit in sleep, and periodically wake up, send current into the strain gauge during a very short time, just enough to take a rough measurement and determine if the user is standing on the scale or not.

If the scale wakes up for 100µs every second, then power consumption will be 10000 times less.

In strain gauge bridges that I have used (120 Ω and 350 Ω) I've tended to excite them with 2 to 4 mA rather than with a fixed excitation voltage and so 1 or 2 mA would flow through each gauge.

Power = $I^2R$ hence, for a 350 Ω gauge it is up to 1.4 mW.

Bridge/Strain Gage Signal Conditioner Omega CAD530.00 DMD4059
Maximum Output: 10 Vdc @ 120 mA

You can operate from 1 to 10V and power is increased with sensitivity accordingly.

Since these sensors are essentially resistive networks, the excitation energy could theoretically be arbitrarily small - in practice, noise, interference, leakage and dry contact concerns, and power requirements of the conditioning circuitry, will dictate the lower limit.