The LPG Gas Monitoring Extension 

Troika Load Cell
Troika Load Cell

Because Liquefied Petroleum Gas is stored in a liquid state the pressure in the storage cylinder remains fairly constant, varying according to temperature and composition (the propane/butane mix ratio), rather than quantity. To determine the quantity of liquified gas remaining we have to weigh the cylinder including its contents, and then deduct the empty weight of the cylinder. The empty weight is always clearly marked by stamped figures on the support skirt of the cylinder.

Can be used with:

The LPG Gas weight monitor consists of 3 load cells elements with a maximum weight capacity of 50 Kgs, that connects to the control unit through an A/D converter.
The load cell measures the total weight of the cylinder, and the gas it contains, and transmits this data to the control unit. 
The control unit adjusts the input data with an internal offset and passes it on to the mobile phone app.
The mobile phone app subtracts the tare (empty weight) as entered by the user, and displays the balance, which is the weight of the gas, on the screen of the mobile phone.
The background colour of the display button will change with the weight of gas displayed:
Above 3 Kgs the background will be GREEN,
Between 1,6 Kgs and 2,9 Kgs the colour will be YELLOW,
Below 1,6 Kgs the colour will be RED.

Sensor Calibration

Load cells resister strain. When they are subjected to a force some surface dimensions change minutely and this change alters their electrical resistance by a very small amount. This change in resistance is made to unbalance a resistor network known as a Wheatstone bridge by a tiny amount (never more than 3 parts per thousand at maximum capacity). The resulting differential voltage is massively amplified and converted to a digital value which can be quantified, stored, and compared to subsequent readings. After installation the load cell's no-load output must be registered in the controller as a zero datum. This is done at the time of manufacture and should never need to be repeated. However if the output on the screen seems hard to believe it may easily be accomplished in the field:  double tap the Gas button on the screen of the mobile phone when there is no weight on the load cell. The phone will buzz briefly and the weight display will go to 0 Kgs, if it is not already doing so. A message will be briefly displayed saying that the sensor has been zeroed. The updated weight info can take a few seconds to be shown. 

Entering the Tare on the Mobile App

The weight shown in the Gas Weight button will always be the weight measured by the load cell minus the Tare, or empty weight, of the cylinder as stored in the app's memory. If the total weight detected by the load cell is 3,6Kgs and the Tare is recorded as 1,2Kgs then the display button will show 2,4Kgs. If you want to display the full weight borne by the load cell the Tare must be set to 0'

To enter the Tare on the mobile app tap the Gas Weight icon on the left of the screen once and within 3 seconds double tap the Caravan Pilot Title.

Setting the TARE
Setting the TARE

Setting Up the Tare.

After tapping the Gas icon on the left of the screen, within 3 seconds double tap the Caravan Pilot Title. A slide control will appear showing the last value of this setting that has been entered. Move the slider to the correct value (max 20 Kgs) as stamped on the gas cylinder added to the estimated weight of the regulator and supported hose, and tap the Title line again to Save.
The Gas button will now display the measured weight of the cylinder with the Tare subtracted. The Saved value will endure until changed.

If the weight displayed is 3kgs or more the background colour of the button will be GREEN. Between 1,5Kgs and 2.9Kgs the button background colour will be YELLOW, and below 1,5Kgs the background colour will be RED.

Peeking the Parameters

Tapping the Gas 1, Gas 2, or Towball weight button once, will briefly reveal the Tare(s), GVM, and Correction Factor that have are stored for the button being tapped, in place of the normal button information display. This is a convenient method of quickly confirming that the correct values have been stored.

Installing the Gas Cylinder Load Cell

There are three load cell buttons in the assembly all of which can support all or part of the weight of the gas cylinder. However only when the assembly is placed i\under the centre of the cylinder will it stand vertically without needing external support, and this is the only position in which all of the weight of the cylinder will be detected.

Therefore you should ensure that when the securing clamp is loosened and the bottle is standing on the load cell assembly there is no tendency for the bottle to lean away from the vertical.

There are a huge variety of gas cylinders available on the market and no two installations are identical. There may be some customising required with a block of wood or some other material to effectively secure the load cell assembly in position under the gas cylinder.

The A/D converter, which is housed in a plastic enclosure a half a metre from the load cell should be mounted on a wall where it will not be damaged using the mounting tape supplied. From the A/D converter there is a 4 metre cable terminated in a 4-pin XLR plug which plugs into a socket on the control unit housing. The socket is clearly marked 'Gas'.

There are always a few seconds of delay between the controller receiving fresh data from the load cell, and that data being displayed on the screen.

Sensor Creep

Sensor Creep refers to the tendency of a load cell to be affected by the weight that is brought to bear on it. Ad the load cell deforms under the weight of its load it will record an increasing over-read error. All load cells are affected by creep to some extent which is why the load should be removed from the cell when it is not being measured. With gas cylinders this is not always convenient since the sensor works under the centre of the cylinder. 

Where the gas cylinder stands freely in a well in the front compartment it can be lifted out and the weight sensor placed in the bottom of the well while it is needed there. If the gas cylinder is held in a band clamp it must be raised by some device to lift it off the sensor, and the clamp tightened to keep it in place.

Dual Gas Bottles

If only a single gas cylinder is in use at any one time and a selector valve switches between cylinders the load cell can be physically positioned under the active bottle.  When the gas selector valve is switched to the second cylinder the load cell can also be moved to take its place under the now-active cylinder. It may be necessary to revise the Tare weight of this cylinder to keep the gas-content information accurate.

When 2 LPG gas cylinders are to be monitored simultaneously the controller may be connected to 2 LPG load cells (in addition to the optional Tow Ball load cell). The Tow Ball Weight button doubles as a control and display button for the second LPG cylinder. In this case both gas weights are simultaneously displayed on the mobile phone screen, except when the right-hand weight button doubles as the tow-ball weight display.

To convert the right-hand weight button to monitor Gas 2 press the Tow Ball button down for at least 5 seconds. The legend on the button will change to Gas 2, and usual Calibrate command and Tare setup becomes operational.

When the tow ball is to be weighed simply hold the Gas 2 button down for 5 seconds and the button will revert to Tow Ball weight measurement.