Water Tank Monitors (Dual)

Flows sensors can be inserted into (max 2) tank outlet pipes to measure the outflow of water from the tanks. The total outflow, as well as the water remaining in the tank, is reported on the mobile phone. Measurement of waterflow continues when the phone is switched off or is out of range. Tank capacity of up to 200L is supported.

 Can be attached to: 

Basic Flow Sensor
Basic Flow Sensor

The control unit can monitor and report on two water tank monitors which are functionally the same. Water passing out of a tank turns a little bucket wheel and fractions of rotation of this wheel are detected, counted and converted to litres of water by the electronics and programming. The flow sensor provides only data on the outflow of absolute litres but, with the help of user supplied data regarding tank capacity, as well as a signal that the tank has been newly filled, the app can report the percentage of tank capacity remaining in addition to reporting the total outflow since last fill.

Flow Sensor YF-B6
Flow Sensor YF-B6

The flow sensors are equipped with a thread of between 1" and ¾" BSP on both ends. There are reducing bushes commonly available at all hardware and builder's shops that bring this down in stages to 1/2 inch and even 1/4 inch, which is adaptable to all types of plumbing that are found in an RV.


The Flow Sensors

The flow sensor measures water flow by means of a bucket wheel or impeller in the water passage that generates Hall Effect impulses when turning at a rate proportional to the water flow. Several hundred of these impulses represent a litre of water passing through the sensor, the exact number depending on the model of flow sensor. Three popular sensors are supported -  the all-plastic FS400A (most often used to monitor tank filling flow), the brass-bodied YF-B6., and the plastic 1/2" YF-S201.

Because these sensor have differing flow rates the controller's firmware is set up to serve one or the other.

Water Flow Monitor
Water Flow Monitor

The only maintenance it will ever need is being cleared of foreign matter clogging the bucket wheel or impeller. 

Excessive Usage Alarm

A maximum limit for continuous flow can be set on the through the app. Once this limit is reached a buzzer sounds and continues to sound until the water flow is shut off. The alarm is sounded by the control unit so, once set up, no mobile phone is required for this feature to work.

Dribbling Tap Detection

Any water flow at or near the lower limit of the flow sensor's measurement range is reported by a buzzer. The buzzer mutes as soon as the flow is shut off or normal rate of flow resumes.

Inflow Monitoring

As sensor can be inserted into the filler hose to quantify water flowing into the tank. When water is added to the tank through the filler neck the influx quantity is deducted from previously recorded outflow. This allows a tank to be partially replenished without losing accuracy in the content calculation. Without this the outflow is zeroed when the tank is completely filled.

When this outflow record reaches zero any further inflow is ignored.

Sensor Accuracy

Flow sensors detect the passage of a fluid by the rotation of a bucket wheel or impeller places in the flow path of the fluid. Since the impeller has almost no mass there is no inertia to overcome and no momentum to absorb when the flow starts or stops, and the inertial error that does arise on start will become a cancelling momentum when the flow stops.  

The impeller offers almost no frictional resistance, and such resistance as does exist is constant, because the flow rate is determined by the water pump and is therefore unchanging, and is factored into the conversion calculation.

Flow Sensor Error Compensation

Over a period of time condition may change within the sensor body. While there may be no visible or measurable wear or clogging, the accuracy may fall outside of the 98% target range. As long as this drift is consistent, which it generally is, a correction factor of between -20% and 20% can be applied by the controller to keeps the accuracy sharp.

The correction factor is easily entered to the app by a slide control and then transmitted to the controller, where it is stored until changed. Both of the pumps supported by the controller can have their individual correction factor.

While the Flow Sensor Error Correction slider is visible the raw clocking data produced by the flow sensor is displayed  on the screen of the mobile phone. When the flow quantity is known by pouring it into a calibrated vessel then the exact rate of clocking from the sensor can be determined and the most effective correction factor calculated.


Clearing the Flow Count

The flow sensor will report every 3,5mL water that passes through it to the control unit. The control unit will add this count to a total kept in memory until the counter overflows or is cleared by instruction from the mobile phone. To keep an accurate track of water usage from a tank the outflow counter needs to be cleared every time the tank is filled. The user does this by quick (< 400Ms) double tapping the Tank Icon on the mobile phone screen. The phone will buzz briefly when the clear command is sent to the control unit, and the water usage total for that tank will reset within a few seconds. 

Water Used & Quantity Remaining

The normal display is for the app to show the percentage of tank contents remaining. While any water tank icon is pressed and held down the app will display instead the actual water drawn from that tank since the count was last cleared, as well as the tank capacity previously entered by the user (see below).

Interconnected Tanks

Where separate tanks feed different outlets (for instance one tank may supply the kitchen whereas the other supplies water to the shower) manufacturers sometimes connect a cross-feed hose between tanks to equalise their contents. This is to prevent one tank running dry before the other. In this case the indicated percentage of water remaining will not be accurate since some of a tank's capacity has been diverted without passing through the flow sensor.

For this reason the cumulative percentage of water remaining is displayed, in parentheses, below the absolute percentage for either tank. To maintain compatibility with single tank systems and to ensure the correct display in parentheses the capacity of the second tank should be set to minimum when there is no second tank. (See below).

Setting the Tank Capacities

In order to successfully calculate the percentage of water remaining the app needs to know the total capacity of each tank.
To set the tank capacity: give the icon for the chosen tank a short (< 400mS) tap. The label for the other tank will go grey for 3 seconds, and during this time double tap the Caravan Pilot title.
A slide control will appear which will allow any value up a maximum of 200 Litres to be specified. Move the slider to the correct position and Save by tapping the Caravan Pilot title again.

If no double-tap on the Title is received within the 3 seconds the opposite tank label will return to its normal state.
Repeat for the other tank. 

When the Controller Loses Power 

Flow Sensor Installed
Flow Sensor Installed

To register the flow through the sensor the controller needs to be powered on. When the controller is without power water will flow through the flow sensor, but without being registered. However during normal operation the controller saves the flow count to non-volatile memory after every 5 litres of flow have that have been observed, so an unplanned power down can result in up to 5 litres of inaccuracy arising.

The latest flow count is also stored to non-volatile memory whenever the mobile phone app is paused or ended, assuming the controller is online to the phone. One of the last things the app does when it is paused or shut down is issue a command to the controller to store flow sensor data to non-volatile memory. Therefore it is advisable to close or pause the app while the controller is online immediately before switching the controller's power off.


As shown in the image at right the flow sensor is easily interposed in the tank outlet pipe using standard plumbing parts commonly available at any building or hardware shop. The sensor can be mounted in any orientation as long as the direction of water flow, which is clearly marked on the unit, is observed. It contains no serviceable parts and requires no maintenance or adjustments.

When Flow Sensors Cannot Be Used

There are water tanks mounted in vehicles that have only a tap as an outlet. No hose and no pump. Sometimes these tanks are transparent, sometimes the are no. Sometimes they are hidden and their content level can only be guessed at.

For these situations we offer an ultrasonic proximity detector that mounts on the tank cap and reports the distance between the  water level and the tank cap. All that is required is that the bottom of the tank is visible from the filler throat, and that the throat is at least 55mm wide. The sensor can be detached from the cap for filling and for transport.

The US Sensor & Mounting Ring
The US Sensor & Mounting Ring
Left Tank Ultrasonic Level
Left Tank Ultrasonic Level

 Tank depth is setup by a slide control and this enables the app to graphically represent the level of water in the tank. The slider control can set up a tank capacity of up to 200 litres or a tank depth of 200cm (2000mm). 

The proportion of remaining water is also presented as a percentage of a full tank.