Liquid Crystal based optical telemetry applied to 4-20Â mA current loop networks

We report on a novel way to interface a liquid crystal based optical telemetry system to existing 4-20 mA sensors and apply it to the specific case of gas sensors. We prove that existing sensor networks can be retrofitted with passive electro-optical transducers and low-power Voltage to Frequency (V-F) converters without any loss of accuracy. In particular, we show that resolutions of 16 bits can be achieved even for short acquisition times and low sampling rates, limited only by the V-F specifications. The proposed approach allows harnessing all the benefits of optical networks, such as increased transmission distance of up to several tens of kilometres and intrinsic safety, without having to redesign the actual sensors.