HDK Position Sensor - circuit suggestion

[brabus]

Good day everyone.

I am developing a new control unit for a rather old engine from Volvo Penta, model DH10A. What's interesting about this engine is the diesel pump: a rotary unit, very similar to the widely used Bosch VP37.

The rotary pump regulates the injected quantity by precisely setting the position of a metal rod, which in turn opens and closes small vanes inside the pump. The position of the rod is sensed by a magnetic sensor called HDK (in German: Halb-Differenzial-Kurzschlussringgeber, in English Half-differential short-circuit ring travel sensor).

A description of its working principle is here: https://de.wikipedia.org/wiki/Halb-Differenzial-Kurzschlussringgeber and here: https://second.wiki/wiki/halb-differenzial-kurzschlussringgeber
Shortly, the movement of the short-circuit ring changes the inductance of the second inductor; by measuring the inductance ratio between L(s) and L0 one can calculate the exact position of the ring. The system is completely free of contact, making it extremely robust and reliable.

This type of sensor seems to be used exclusively for this application. I cannot find useful material anywhere. All we know is that BOSCH developed an IC, named CC215, which could translate the inductance ratio into a DC voltage to be fed to the ECU electronics in order to measure the position of the rod.
The working principle is depicted in the attached image:


The IC is obsolete and there seems to be no alternative on the market. I am developing a discrete version of the functions, but the accuracy will be nowhere near the 12-bit an IC can achieve. For my application, 8-bit will suffice, but still the issues with offset, noise and thermal drift are non trivial.

Any idea and suggestion from your side will be highly welcome. Thanks in advance!

[MichaelPI]

Do you have to fulfill automotive requirements (AECQ100 mandatory) or is it for hobbyist use only?

The LDC1612 could work, if the two sense coils have two connections each (no center-tap). As the measurement of the inductance is based on the resonance frequency, the bandwidth of this solution could be a bit too low for your purpose. The tank capacitors would have to be closely matched and temperature stable (e.g. NP0). You would need in addition a microcontroller to perform the ratio calculation and a DAC to generate the analog output signal.

As an alternative: Half-bridge LVDT signal conditioner like AD698 from Analog Devices.

[ace1903]

When compared with the attached block diagram AD5933 has a similar structure. It is worth checking if it can be used.

[Terry Bites]

I think emulating this IC is hard work. I'd be thinking about using DDS , some high reolution ADCs and a uC. Still hard work!

[brabus]

Thank you for your suggestions and for your time.

I ended up choosing a software approach, based on an STM32 platform. Wish me luck!

[dhivith]

We are developing the HDK sensor for our Actuator position sensing application @brabus can you help use out with the Circuit and did you find satisfactory results using the software approach, based on an STM32 platform?

[brabus]

Good morning dhivith,

Yes, the results have been satisfactory, the application is running flawless in the field.
The methodology we developed required extensive research, careful analog design and a number of tricks in the software.

We are not disclosing the details of the implementation, given the investment it required. We will be glad to offer the package solution based on a commercial agreement; let's discuss the details in private.

Thank you and best regards.