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We are using an inductive coil transformer for a sensor. We excite the signal with a low frequency (1kHz-3kHz), and what we measure on the secondary indicates the proximity of a part.

Generating the signal and receiving the secondary signal has been completed, but one important feature we absolutely need to figure out is how to in circuit detect if either of the coils has been disconnected.

A simplification of the overall schematic : enter image description here

Any suggestions on what circuitry we could add for coil detection? DC offset does not effect the performance of the transformer sensor.

Thank you

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Sensing the current thru the primary is the obvious way to detect whether it is present. All you need is a small current sense resistor. It looks like this could be on the low side easily enough. Amplify that and look at it during the peak of the 2 kHz drive signal. If it's not high enough, then assume the primary is open.

For the secondary, maybe your receiving circuit can pass a little DC current thru the coil. That should be irrelevant to its operation, but would allow you to sense its presence, whether it is receiving any AC signal or not. Something as simple as a high-resistance pullup on one end with the other end grounded would do. If the DC voltage ever went high on the pulled-up end, you know the coil is open.

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  • \$\begingroup\$ I can definitely use that method for the primary side. The issue I have is when the part that we are detecting is in the middle of the transformer, the amplitude of the signal coming out of the secondary is ~0Vpp . \$\endgroup\$ – Alex Bussiere Jan 3 '18 at 13:48

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