Beier Electric FP-10 Currrent Sensor


I have used a Beier Electric FP-10 Current sensor with Primary current 30A and secondary 0.333V to read the IRMS using the EmonLib and the setup provided for using CT Sensors - Interfacing with an Arduino. I have worked out the although I am unsure of the number of turns on the coil. I have worked the burden resistor and also did some calculations and found out that my Primary Peak Current is 42.426A, my Secondary peak Current is 0.07071 and my SPC is 33.35 ohms. therefore i have set emon1.current(1, 60);. i don't get any real results just some fuzzy numbers... how can i connect this sensor and interface it with my Arduino Uno  and get my desired results??? Right now i am using the schematic and code provided by

Robert Wall's picture

Re: Beier Electric FP-10 Currrent Sensor

Because the  CT output is defined as a voltage, it means that it has a built-in burden resistor. You can find how to calculate the calibration coefficient on the Building Blocks page about calibration theory - the part about voltage output CTs is at the end of the CT section. 

However, as your CT output is only 0.33 V rms, and I presume you are using an Arduino with a 5 V supply and 5 V analogue input range, you are only using less than 20% of the available input. That means when you measure current below approximately 1.5 A, accuracy will degrade significantly.

You could amplify the CT output to bring it up to the amplitude that the analogue input expects (which of course would mean that the calibration constant changes to compensate).

christkyp's picture

Re: Beier Electric FP-10 Currrent Sensor

Thank you for your response Robert,
is the setup provided in this link still the same for my FP-10 CT? But without the burden resistor? Also how can i amplify the ampliture of the analog input? Because the calibration steps are more than one section in this link:
hank you in advance.

Robert Wall's picture

Re: Beier Electric FP-10 Currrent Sensor

If you are not using an amplifier, the basic way of connecting a CT is the same. All the burden resistor does is convert the current output of the CT into a voltage. (The burden is still connected in the same place electrically, it is just inside the housing in yours.)

If you need to add an amplifier, then firstly you need one that will operate on a single supply of 5 V. You can use either the inverting or the non-inverting configuration but you will need to take the earth shown in those diagrams to the junction of the bias resistors, not to the 0 V of the supply. You need a gain as close to but not greater than 5.3. Suitable E12 resistor values: Rin = 2k2, Rf = 10k; or R1 = 2.7k, R2 = 10k, but if E24 resistors are available, you can get closer to the required gain.  One side of the CT connects to the bias midpoint as before, the other side to the amplifier input (marked Vin), and the amplifier output goes directly to the Arduino input pin.

For the purpose of calculating the calibration, the CT voltage you use will then be the amplified voltage.

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