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Gas Meter Calibration System

The ‘Calibration Standard’ of the Test Bench is “Bell Prover” which is considered a Primary (Calibration) Standard or “Sonic Nozzle” the best Flow transfer Standard, to Test & Calibrate Domestic Gas Meters (Gas Meters used in Hotels/Restaurants etc.). The device is ideal for OEMs, Calibration Laboratories & Calibration Service Providers

Bell Prover

Bell prover helps the gas flow meter test bench to sample and calibrate the gas flow. It can test rota meters, domestic gas meters, and other forms of low range gas flow meters. The bell prover can move up and down automatically and the gas-output valve can be switched automatically.

The liquid cell inside the Bell forms a sealed space of variable but calibrated volume. When the Bell moves down into the sealed liquid, the gas in the Bell is exhausted to the flow meters (UUT) through a Flexible pipe. The exhausted gas volume will be detected compared with the cumulative in the meters. – mainly used for calibrating Domestic gas meters G1.6 to G16.

Sonic Nozzle

A “sonic nozzle” (also known as “Critical Flow Venturi” or “Critical Flow Nozzle”) is a flow meter that can be used as a calibration standard for gas flow meters or any flow measurement device. By design, sonic nozzles are a constant volumetric flow meter.

The nozzles are designed and manufactured to the ISO standard and as such the gas is accelerated along the Bell Mouth converging section and then is expanded in a conical diverging section, which is designed for pressure recovery.

In the throat, or minimum area point of the Sonic Nozzle, the gas velocity becomes equal to the speed of sound. At this point, gas velocity and density are maximized, and the mass flow rate is now a function of the inlet pressure, inlet temperature, and the type of gas.

Sonic nozzle produces very stable flow

Highly desirable characteristic in a flow rate

No moving parts which affects reliability

Mass Flow Varies Linearly with Inlet Pressure

Minimum Upstream Piping Required

Long Term Accuracy

Tailor made for customer’s exact requirements

Wide range of meter sizes calibratable from G 1.6 to G400 (and above)

Highly sophisticated designs to enhance operations and increase customer’s throughput

According to the UUT bell prover based or Sonic nozzle based or meter to meter comparison systems can be selected

Follows to ISO-9300 standard

Available with multiple levels of autonomy including Manual, Semi-Automatic or Fully Automatic methods of operation

Meter Sizes G 1.6 to G400 and above
Flow Rates 1 LPM to 10000 m3/Hr
Lines As required by the customer (1, 2 or 3)
Calibration Campaign Time > 60 sec
Calibration Methods Bell Prover Method
Sonic Nozzle Method
Comparison Method
Calibration Accuracy 1% to 0.3%
Calibration Media Air (Density correction factors can be given for other gases)
No. Of Units under Test 4 at a time using bell prover and 1 or 2 according to line sizes for sonic nozzle
Control Console To incorporate all process indicators. Higher powerpanel will be seperate if necessary
Method Of Operation As required Manual, Semi Automatic & Automatic
Clamping methodes Pneumatic only


Control Panel

Reducers / Expander



Weighing Scales

Storage Tanks and more

CALFLOW Software

Mounting Clamps


A Gas Flow Meter Calibration System is a specialized tool used to test and calibrate gas flow meters to ensure their accuracy and reliability in measuring the flow of gases.
The two common methods are the Bell Prover method and the Sonic Nozzle method.
The Bell Prover is a calibration method that uses a bell-shaped vessel to displace a known volume of gas under controlled conditions. The volume displacement is used to calibrate the flow meter.
Most commonly, the Bell Prover method is used for calibrating positive displacement meters, such as rotary and diaphragm meters.
It works by allowing gas to enter the bell, which displaces the bell upward. The volume displaced is known, and the time it takes to displace this volume is used to calculate the flow rate.
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