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Water Meter

  • Josef Konrad
    Josef Konrad on

    My water meter

    I’ve acquired a Penta with one of these installed. There’s no info on it’s source, and my son want one because it works extremely well.

    Before he steals it in the night can someone tell me where I can get him one?

    Many thanks

    Simon Tasman
    Simon Tasman on

    You put behind the CaravanPilot title that you see in the image you posted.

    As in:

    And you see the whole wide range of the stuff they make.

    Sometimes you have to wait in line, I hear, due to supply chain hassles from China. So be patient.

    Josef Konrad
    Josef Konrad on

    Thanks for that link. Amazing product line.

    I  especially like the device that sends you an sms when the power goes off and when it comes on again.  Only useful in South Africa, but almost essential if you want to know whether you’ve got power when you get home.

    As you said, supply is short. But I’ll look out for a second hand unit

    Fyko van der Molen
    Fyko van der Molen on

    Caravan Water Meters.
    Many caravans and camping trailers use the otherwise wasted under-floor space to mount one or more water tanks. Because the shape of these tanks are necessarily broad and flat the most practical way of determining the state of their contents is to measure outflow. The outflow count is reset to zero when the tank is filled and thereafter the quantity withdrawn is subtracted from the known maximum capacity and the remaining can be displayed on a mobile phone app or a dedicated LCD-type display unit. The transmission to a mobile phone uses the phone’s Bluetooth channel which has a range of up to 30 metres.

    The flow sensor has a bucket wheel in the flow path and transmits up to 500 electronic clicks per litre to the electronic control unit, where they are converted into litres drawn and saved in memory in case of power down and made available for display. The sensor is inserted into the hose between the tank and the pump, not after the pump, for two reasons. Firstly the low water pressure there means that leaks are less likely to arise and, secondly, the rush of water drawn by the pump immunises against errors caused by ultra-slow dribbles from a leaking or not properly closed tap.

    For trailers that are equipped with 2 tanks, each with its own outflow and pump, the system caters for 2 flow sensors and 2 maximum capacities. Each sensor has its own outflow count and percentage remaining available for display and, where the tanks are interconnected, the global percentage of capacity remaining is also calculated and displayed.

    The accuracy of the bucket wheel sensors is better than 99%. Typically a tank of 150 litres capacity will show less than 1 litre of error when the water is exhausted.

    Overlander Water Meters.
    Overland vehicles are often equipped with taller water tanks that have no pump but deliver directly through a tap on the side of the vehicle. In this case there is no pump and no hose – water flows through the tap by gravity only. When these tanks are not easily visible the level of contents can be measured by an ultrasonic transceiver that pings the water surface from above and measures the time taken for the sound pulse to make the round trip.

    The accuracy of the result depends on timings within the control unit but is never less than 30mm. When the height of the container is known the remaining water can be shown as a percentage of the total capacity. In this case there is no need to reset anything when the tanks is filled.

    Campground Tanks.
    The ultrasonic capability has been extended to cover larger water tanks such as those used to store borehole water or captured rainfall. The contents of these tanks may vary unpredictably and be difficult to determine from a distance.

    Because of the greater distance reporting is via point-to-point continuous radio transmission and the control and display functions are vested in nodes attached to the establishment’s WiFi LAN. The distance from the tank to the base node can be more than 2Kms. In addition to the ultrasonic scanner the remote node can measure weights up to 2 tonnes, read 2 digital thermal probes, monitor 2 digital switches, and control 2 output relays.

    The display of node data (water level, weight, temperatures, switch and relay states) can be displayed on an LCD-type unit at either the remote node, or the base node, or both. Additionally this current data can be placed in the establishment’s web domain, from where it can be displayed on any mobile device anywhere in the world that has network coverage. Also displayed is the radio signal strength received at both ends of the radio link.(Shown below).

    The mothernode on the LAN that receives the input from the remote tank node can process an algorithm whereby the pump is say switched off when the tank is full, or the outlet is adjusted when the tanks is nearly empty. The other inputs and outputs can similarly be user-programmed to perform automated functions.


    For images pertaining to the caravan/camping water meters see and follow the Caravan & Camping menu. For more info on the campground tank follow the NodeStar menu item.

    Fyko van der Molen
    Fyko van der Molen on

    We’ve recently added 2 features to our caravan water meter:

    1. Excessive draw alarm. A buzzer sounds as soon as the last continuous water draw exceeds a user-defined limit. The limit can be anywhere between 1 and 20 litres.

    2. Drip alarm. A buzzer sounds when a very slow flow rate has been detected over a period of time, indicating that an outlet somewhere is not completely closed. Nothing to set up here – it’s all automatic.

    All existing units in the field can be upgraded at minimal cost. The firmware upgrade is free but there is a buzzer and a housing which have a small price tag.

    Simon Tasman
    Simon Tasman on

    So as I understand it, it can:

    1. Measure and report the outflow from 1 or 2 tanks,
    2. Measure inflow through the filler and adjust content record accordingly,
    3. Report the water percentage of resource remaining in 1 or 2 tanks based on user-defined tank sizes.
    4. Combine these when tanks are interlinked,
    5. Alert when a user-set outflow limit is exceeded,
    6. Halve the alert level when less than 20% remains,
    7. Alert when water remaining drops below 20% of capacity,
    8. Alert when there is a slow dribbling outflow.

    Have I left anything out?


    Fyko van der Molen
    Fyko van der Molen on

    For now that’s all it can do with the water tanks. But we add stuff from time to time.

    Apart from the water stuff it can also weigh the gas bottles, the tow ball, and the main wheels.

    And then there’s the digital thermometer for the fridge or whatever.

    Josef Konrad
    Josef Konrad on

    Why have an inflow meter when you can just zero the outflow register when you fill the tank? It takes exactly 3 seconds to do that and it’s failure-proof.

    Fyko van der Molen
    Fyko van der Molen on

    When filling from a hose it’s definitely best to zero the meter. It’s quick, easy and removes any accumulated errors.

    But imagine the guy in the bush that fills a couple of buckets with rain water runoff from his tent roof or awning. It’s clean enough water to wash with, but it’s not enough to fill the tank – so he can’t zero without introducing a huge error, and if he pours it into the tank he generates a big error in the other direction.

    So if he has an inflow meter, he pours his buckets into the tank and his tank content meter stays accurate to within a few tenths of a litre. (Find that on any other water meter anywhere in the world.)

    Fyko van der Molen
    Fyko van der Molen on

                   Flow Sensor Accuracy

    Over a period of time the clocking rate (the ratio of signal transitions to a litre of water) of flow sensors can change, leading to an annoying loss of measurement accuracy.

    Opening the sensor reveals nothing – there is more measurable wear and no clogging or resistance to the movement of the waterwheel, the part that does the metering. The waterwheel is turned by the movement of water without ever blocking or interrupting the flow – the water can easily bypass the wheel entirely, so it’s a question of the friction of the wheel on its axis. Something that is too small to measure, and only shows up in a slightly reduced rate of movement – which results in a loss of accuracy of up to 10% in extreme cases.

    To remedy this without changing any parts os spending any money we did the following:

    1. The outflow count up to 10L shows whole litres as well a a decimal thereby making for 100 discrete steps for the first 10 litres of outflow. You can read with a resolution of 1% how much it takes to fill a calibrated 10 litre bucket. (empty five 2L Coke bottles of water into a bucket and mark the level). If the error is less than 1% there is no error.
    2. We introduced a user-calibration facility whereby the user can modify the outflow count between -20% and +20%. This calibration factor is remembered indefinitely but can be changed anytime it’s required to do so.
    3. For ultra-purist power users there is the facility to display the raw clocking data as received from the sensor. With this the actual clocking rate can be calculated the better to define a calibration modifier.

    With these additions the life of the flow sensors is extended indefinitely and users are able to adjust their meters to an accuracy of 1%.

    Since there is no hardware required this update is free to all existing users.

    The image shows the decimal place in the outflow count and the raw clocking info in the lower line

    WaterWatch Display

    Josef Konrad
    Josef Konrad on

    I have found that the intake sensor is most prone to inaccuracies.  A lot seems to depend on the rate of pouring the bucket into the inlet pipe, the slower the more susceptible it is to overreading.

    Fyko van der Molen
    Fyko van der Molen on

    If you use a wide-bore inflow sensor and your inflow is quite slow it is possible for air bubbles to pass through the throat of the sensor and be interpreted as water.

    The sensor already constituted a partial restriction, since its throat is narrower than the 40mm pipe that’s normally used from the filler neck, so with a little dexterity you can keep the filler pipe above the sensor filled with bubble-free water. We use a 60Lpm sensor to take advantage of the large-bore inlet pipe.

    If you can’t manage this reliably then you can introduce an even narrower restriction below the sensor to keep the water backed up above the sensor more readily. This will result in slightly slower filling off course.

    Using a funnel with a wide outlet and a little practice it’s quite easy to keep the sensor well-supplied so that it doesn’t swallow air with the water inflow.

    Fyko van der Molen
    Fyko van der Molen on

    The water meter always had the ability to weigh gas bottles, the jockey wheel (for conversion to tow ball weight), and even the main wheels but, since they were used in different contexts, they have often been used for only a single purpose.

    As a water meter it typically gets attached to a wall from where it is easily seen by someone drawing water, whereas the weight gauge gets moved around to wherever it happens to be needed.

    Amongst the fastidious these is an increasing concern about weights in general. Tow ball weight (as extrapolated from jockey wheel weight) has long been a concern, but there’s an increasing concern about what all the add-ons to the tow vehicle are doing to its gross weight.

    Weighing wheel by wheel works OK but it’s laborious and getting the load cell placed just right can be a pain.

    With this in mind we’ve developed a jack-top bracket that allows an entire axle to be weighed at a time. Individual axle weights are at least as useful the combined total because you can figure out each suspension is taking the strain.

    The jack-top brackets make a very stable platform for measuring axle weight and we’re happy to suggest a safe design but, due to the large forces involved, we don’t actually supply ready-made brackets. Your local boilermaker’s workshop will be able to do that for you.

    Fyko van der Molen
    Fyko van der Molen on

    This is what a Nissan NP300 back axle weighs with an aluminium canopy fitted

    Dan Perkins
    Dan Perkins on

    Can that axle load cell still weigh a jockey wheel accurately?

    My towball weighs less than 100Kg.

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