At the petrol pump, fuel measurement is primarily performed using specialized flowmeters to ensure accuracy and fair dispensing.
Petrol pumps measure fuel by using petrol flowmeters which are PD flowmeter types. This technology is crucial for precisely tracking the volume of fuel delivered into a vehicle's tank.
How PD Flowmeters Work
PD stands for Positive Displacement. Unlike some other flowmeter types that infer flow rate from properties like velocity or pressure, positive displacement flowmeters directly measure the volume of fluid passing through them by trapping successive volumes of fluid and counting them.
Here's a simplified breakdown:
- Segmentation: Inside the PD flowmeter, there are moving components (like pistons, rotors, or vanes) that divide the continuous flow of fuel into discrete, known volumes or segments.
- Counting: As the fuel flows, these components move, and each movement corresponds to a specific, measured volume of fuel that has passed through. The flowmeter mechanism counts these movements.
- Calculation: The total volume dispensed is calculated by summing up the count of these discrete volumes.
Setting the Dispensing Target
The process begins when the customer specifies the amount of fuel they want, either by volume (litres) or by cost (currency).
- Operator Input: The petrol pump operator (or the customer at self-service pumps) sets a currency/litre based setpoint on the pump's console. This tells the pump the target volume or value for the transaction.
- Instantaneous Calculation: As the fuel flows, the PD flowmeter calculates the volume dispensed instantaneously. This allows the pump's electronics to monitor the progress against the setpoint in real-time.
- Stopping the Flow: When the total calculated volume reaches the setpoint (or the corresponding currency value), the pump automatically stops dispensing fuel.
By segmenting the total volume into smaller, measurable segments and counting them, the PD flowmeter ensures an accurate measurement of the dispensed fuel litres. This method is highly reliable for commercial applications like fuel dispensing at service stations.
