Sunday, 5 August 2012

Tank Watch Monitor

Boredom forced me to install the Dometic Tank Watch Monitor today.  My original plan was to get one of the marine engineers to fit it, but early in the day I thought “Have a go!”   There was one monitor left in the chandlery and I booked it to Waiouru before carefully unwrapping all the components.  First task was RTM (read the manual).  It’s something I’m not usually very good at so I carefully read it twice.  There are two parts to the monitor.  The gauge and the sender unit.

“Exterminate.. Exterminate” OK… Jan thought the probes were from a Dalek!

The sender unit has three probes of different lengths.  Two of them are made from flexible plastic tubing.  Each probe has a sliding float on the end which contains a small magnet.  Inside the tube are two wires.  When the float rises the wires connect forming a circuit which lights up on the gauge.

My first task was to carefully cut the plastic probes to the required length without severing the thin wires inside. 

As you can see from the above photo we have a large; but shallow tank.  The three probes give us four LED lights on the gauge.  If the tank is empty then all the floats will be down and a green light will appear on the gauge.  As the tank fills each float will rise and the LEDs on the gauge will change colour.  The “Full” probe is the shortest.  There is actually another 2 inches of capacity in the tank and because our tank is so large we should have plenty of time to arrange for the tank to be emptied after the gauge reads full.

Having done the difficult part it was only a matter of screwing the sender unit into the tank mounting block and wiring it up.

There are only four wires (three probes and a common negative return) which had me hunting through the workshop for some four core flexible cable.  I could only find 7 core cable which means we have three spare wires.  The probe wires have been connected to the multi-core cable with bullet connectors.  This will make it easier to disconnect the wires if when the sender needs to be removed to clean the probes.  I know they are likely to eventually “clog-up” with the contents of the tank! 

The individual wires at the other end of the multi-core flex have been labelled but not connected to the gauge.  I want all the gauges to be present and fitted to the instrument board before I attempt to construct the wiring loom.  The last task was to tidy the wiring.

The afternoon was spent sanding down the inside of all the new cupboards before applying a coat of varnish.  Our intention is to apply two coats of varnish to all the concealed timber as the build progresses.  This should reduce the time it takes to do the final application, which we hope will be confined to all the visible timber.  We’re going to let the joiners give Waiouru it’s final coat of varnish.  The fumes can be overpowering and we may just plan to be away from the boat for that day and the subsequent night.

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