UniMeasure Linear Position Transducer used for Underwater Depth Measurement

Under water depth measurement with draw wire transducer

It probably goes without saying that there are very few linear position transducers that can withstand being submerged in 20 metres of water. And if you did come across such a device it would be very expensive.

However, there is a much more practical solution available that is very affordable, as one customer found when they contacted ADM Instrument Engineering and asked if we could offer a solution to measuring the depth of their underwater sweep rig.

Naturally, any solution was going to have to be highly resilient to water ingress, as well as extremely reliable. A big concern with any marine application is avoiding water ingress whilst devices are subjected to the high pressures experienced deep underwater.

With this particular project the depths involved ranged up to 20m. As any scuba diver would know, the water pressure at 20m will cause damage to the human ear, if the diver hasn’t equalised properly.

ADM’s Solution

The UniMeasure HX-P420 is a draw wire transducer that is available with measuring ranges of up to 50m, and an IP68 ingress protection rating.



Because of the nature of its design, the HX-P420 can be mounted away from the ‘action’. In other words, it meant the transducer could be mounted on a part of the rig above water. The IP68 rating ensured that any water splashing on the device could not penetrate its enclosure and affect its operation.

UniMeasure offers an optional stainless-steel rope and this was selected to prevent the sea water causing any corrosion.

The HX-P420 utilises the industry standard analogue 4-20mA output, which means it can be used with higher level PLCs and control systems, or more localised controllers and display units, for example the Eurotherm 32h8i/AL universal indicator. Other output options are also available including 0-10V, 0-5V digital and ratiometric.

Eurotherm 32h8i AL Process Indicator and Alarm


Unlike other depth measuring solutions, such as laser and infra-red beams, steel rope cannot be reflected by light. So, as well as being highly robust the UniMeasure HX-P420 also offered our customer a highly reliable solution.

If you have a challenging linear position measurement problem call ADM Instrument Engineering on 1300 236 467.

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18 December 2018