I think this LM331 can idealy do the job in your application! Use the best capacitor available and adequate power supply decoupling (RC-filters), though.

These type of circuits dealing with a frequency as response to a voltage, or vice versa, work very well if the signal to be transformed is static. If signal is changing, then unwanted signal artefacts are produced! Without any calculation it should be clear, that the frequency of signal change must be much lower than the used frequency of the part.

So, whenever you signal changes very slowly, as in your case with the rather inert mechanical system (I guess??) LM331 will show very nice results. But in another application in which often a LM331 or similar was used to simplify the transmission of analog signals, this can result in trouble. I talk here about the problem to transmit analog signals along long cables in noisy environment. For this purpose often an LM331, SSM2031 or similar was and is used. In such cases often a design is used, where 0V represents 0Hz and let's say 1V represents 2kHz. It's clear, that the signal must only change very very slowly, if it is arround 0Hz, respectively 0V!

A better approach is to use an offset, so that 0V does not represent 0Hz, but maybe 1kHz. So, you would finally have the representation: 0V <->1kHz and 1V <->2kHz. Then, you can allow rather fast signal changes even at very small signals.

Unfortunately, such a design using an offset tends to loose the intrinsic high precision of LM331 due to the efforts of producing the offset.

Neveretheless, at a time when enough precise ADC/DACs were very expensive, LM331 and similar were a wellcome alternative. But today it might be simpler to design a digital solution.

Hope you are fine in Chennai,
Kai