# L37S100S05M-ND response

I’ve got an L37S100S05M-ND 100 amp current sensor and it responds as it should. With no current it reads about 2.45 volts and the signal goes above or below this as the current changes direction. I need the calibration or transfer function for this sensor, i.e. how will the voltage reading change with current in amps?

Greetings,

I’d read the datasheet to indicate that sensor develops a 625mV output swing in response to nominal full-scale current, plus an offset term and 15mV allowance for other errors. This output would be measured relative to the Vref terminal in order to accommodate bi-directional current flows with a single-supply sensor.

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Hello Zack,

The ideal transfer function is:

\textcolor{red}{V_{Out} = 2.5 + 0.625*\dfrac{I_{measured}}{I_{PN}} }

where

• \textcolor{red}{I_{measured}} may flow in a positive or negative direction

• \textcolor{red}{I_{PN}} is the Primary norminal [SIC] current which for your L37S100S05M is 100 A

There are complication that you will need to address. For example, you already know that your particular device idles at 2.45 VDC. While that doesn’t appear to be a big voltage, the algebra tell us that you now have a -8A error with no current flow. One way to eliminate this error is to include a routine that removes the DC offset each time the microcontroller / PLC is powered on.

There may also be an issue with core hysteresis. Recall that hysteresis is residual magnetism that remains in the core. It’s like winding an electromagnet on a screwdriver. The screwdriver will tend to remain magnetized in the direction of the last coil activation. For your application the reading may not return to zero after 100 A. This is an important datasheet parameter know as hysteresis error. For your device it is defined as less than 20 mV given a 0 A \rightarrow 100 A \rightarrow 0A sequence. The algebra suggests an error of 3.2 Amps.

Best Wishes on your design. Please share your results as it sounds like you have an interesting application.

APDahlen

P.S. FUN FACT: To increase the resolution of a current sensor such as this you can pass multiple winding through the aperture. For example, three windings through this device would result in 33.3 A full scale. This can be useful for measuring low currents.

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