Introduction: Cost Effective Watchman Niveau Power Tube Substitute
Replace that expensive Watchman Power Tube with something easier to deal with and cheaper.
For those that don't know, a Watchman, specifically here the Watchman Niveau is a measurement device to provide you a reading on the heating oil level in your tank. It uses a sonic echo detection method in a tube to determine the oil level. it then uses an AM radio transmission to communicate it's measurement to a plug-in receiver you have in a convenient location, which displays the level on a scale of 1 to 10. the receiver is mains powered but the transmitter requires a battery pack. this pack is called the Watchman Power Tube. naturally when the receiver no longer receives a signal it's likely because the power tube battery is depleted and requires replacement. The cost of a replacement is, shall we say, when you consider what it is, exorbitant.
When I say exorbitant, consider you can be paying up to £40 or more to basically replace 4 AAA cells. Now I don't know about you but I don't think that's value for money.
Step 1: What's in This Power Tube Then?
If you follow this link to YouTube, you'll see someone teardown the power tube unit.
It basically consists of:-
4 AAA cells (Duracell Procells no less)
Approx 200mm length of 15mm copper tube
15mm end feed stop end
Male TNC connector
A Label - warning you to use only genuine parts (Ha!)
A small amount of grease.
Now you can perform the same cell change operation that our friend did in the video but I wanted to change the design a little to something more convenient.
You could even try to manufacture the device yourself, and I tried, but a knowledge of how to anneal copper tube when trying to push in a machined down TNC connector is required, so it's a bit of a faff and not necessary.
Now Sensor Systems, the manufacturers, may argue that the Power Tube is designed to be robust, particularly if you have a ham fisted oil delivery technician, but I think suitable placement of the battery back is sufficient to mitigate this.
I was concerned that the use of a copper tube was in some way connected to the AM transmitter method, but my testing indicated that this was not the case.
Step 2: Parts
So to replace the Power Tube, here's what I used:-
4 AA Enclosed battery box with switch, like eBay item 201985066419
Some Lucar (spade) male and female connectors
length of coax, 75 or 50 ohm is fine
TNC Male connector, such as eBay item 222098609573
Some Heat shrink
The Velcro attaches the battery box to the top of the tank.
The Lucar connectors make the connection between the battery box flyleads and the coax cable.
The heatshrink protects the connectors.
The AA box provides a convenient switch (for resetting) and larger than AAA batteries for maybe a bit of extended life.
Step 3: Improvements
So naturally having made the first one my mind starts contemplating how to improve upon it.
First replace the TNC connector with a TNC to RCA Phono adaptor, like eBay item number 222305066327. This will provide a convenient break point to allow you to remove the battery pack to a convenient location for battery swap.
Change the connection on the battery box flyleads to RCA phono termination.
Ensure there is enough flylead length to mount the battery holder away from the oil tank filler neck, but conveniently reachable under the oil tank bund rain cover.
Step 4: Finished and Working
So there you have it. I've hacked my way past Sensor Systems money making scam to get people to part with nearly 40 quid to replace 4 common or garden alkaline batteries, and connect them with an RF connector that hardly anyone uses these days.
Cost of parts used will depend on whether you use AliExpress or eBay or in my case CPC Farnell in Preston which totaled around £2.50 excluding batteries and coax and shipping.
2 years ago
Hi, which way around did you solder the battery pack cables to the coax - don't want to get the polarity wrong and don't have a spare copper pack to check!
Reply 2 years ago
Hi, I followed the convention of the coax cable and plug, so the centre conductor inthe cable and the plug is positive and the outer shield and plug body is negative or ground.
Question 3 years ago
Hi there how did you connect the lucars to the co-ax cable please
Answer 3 years ago
Hi, just by stripping the cable back to reveal a sufficient amount of the copper, like and inch or so, then twisting and folding over to achieve a suitable thickness for the crimp to grab onto.
A bit of solder can help as well to make the twisted wire a bit more robust.