Cleaning Aquadopp/Profiler Pressure Sensors

Recently we received the following question

"On a new subject of pressure sensors. Could yourecommend a cleaning procedure for the sensors. I am a bit reluctant to do to much cleaning around the sensor as I don't know how easily they can be damaged. "


In terms of a cleaning procedure for the Aquadopp and Profiler, I suggest that you remove the cover to the pressure sensor and then check the sponge. If this is soiled, clean or replace it. The sensor itself lies behind this and should only be flushed with water. The metal encasement for the pressure sensor is very thin and therefore susceptible to damage.

-Torstein

Cleaning pressure sensors -

These have been a pain for me for some time. Here is a very useful tip I received from the guys at Valeport. Use a kettle descaler, which you can buy in the UK from most supermarkets for removing limestone deposits from electric kettles and coffee machines. I believe the products offered for cleaning dishwasher machines are similar. UK brands include "Scale Away", "Calgol", Oust All purpose descaler. I have also seen suggestions of using white vinegar, but not yet tried it.

When using a NDP or Aquadopp in a high sediment area I have had units returned with a dried up solid plug of sand inside the pressure sensor cavity. By the time the units get back to our workshop this is very hard to clear without damage to the pressure sensor. Because the pressure sensor is upward-looking, even the sponge fitted inside this cavity gets compressed and does not seem to serve much use. We have adapted all our NDPs by threading the housing cavity and fitting a nylon M16 bolt which has been drilled (3mm dia) along the inside of the threaded portion half-way into the head with a cross hole across two faces of the head. Before screwing this into the cavity, we fill the cavity with Dow Corning 704 silicone oil. So there is no water in contact with the pressure sensor membrane, and the pressure port is horizontal so it does not silt up.

On Aquadopps I have found that the black "button" cover over the pressure sensor frequently becomes loose and often units come back with this missing.

For our Aquadopp units I intend to look into an arrangement like Valeport use for their wave/tide gauge. This uses a plastic fitting screwed into the body with a short piece of plastic capillary tubing (heat)set into a coil and filled with the same Dow Corning 704 silicone oil. Suitable fittings are probably in the Cole Parmer catalogue. As a retro-fit we should be able to do it for less than GBP5 in parts and half an hour of labour. When we do it, we will report back.

Note that all Paroscientific Digiquartz precision pressure sensors use an oil-filled capillary tube and do not expose the pressure sensor face directly to the sea.