Everything You Need to Know About Rotary Gas Meters

What Is a Rotary Gas Meter?

Rotary gas meters trace their beginnings to the early 19th century. Back then, people used rotary meters as water pumps, but it wasn’t until the 1900s that the gas industry warmed up to them. Today, rotary piston meters have become a precise instrument designed to measure gas flow, typically in the 1,000 to 38,000 cubic feet per hour (CFH) flow capacity range.

Because of the way they are designed, rotary gas meters can handle higher volume and pressure than diaphragm meters. That makes them ideal for medium pressure application – 0-175 psi for regular pumps, but that can stretch to 0-1,480 psi for high-pressure models.

Rotary meters are a favorite of gas utilities for billing in industrial and commercial applications. Easy to install, maintain and test, rotary meters are reliable and offer the best accuracy range for low to high-capacity requirements.

How Does a Rotary Gas Meter Work?

As mentioned previously, rotary gas meters work using the positive displacement principle. The rotary gas meter physically separates the intake into exact quantities and measures them individually, allowing precise total flow value recording.

The meter consists of a semi-cylinder cavity inside which are two rotating figure-eight impellers positioned 90 degrees in relation to each other by precision timing gears. These impellers rotate in opposite directions to each other due to the pressure drop across the meter created by downstream gas consumption. As it rotates, each impeller traps a finite and identical volume of gas. The final volume displaced by each revolution of the impellers is transmitted to a final readout module.

Difference Between Rotary Gas Meters and Other Gas Meters

A rotary meter uses the same principle as diaphragm meters but can measure higher volumes and pressure. However, a diaphragm meter has better turndown (~100:1) than rotary gas meters (~50:1).

Because of this, rotary piston meters are usually used in large, demanding industrial applications which diaphragm meters cannot handle.

While turbine flow meters and rotary meters can measure gases at extremely high pressures, turbine meters are a velocity type of meters. That makes them better suited to measuring the highest-pressure gas at the highest flow rate, although they also have a low turndown (~20:1).

Turbine gas meters measure gas indirectly, while rotary meters directly determine the gas flow rate by dividing the gas flow using the rotary blades.

Similarly, ultrasonic flow meters measure gas flow indirectly using sound waves. When gas flows through the pipe, there is a change in the reflected wave, which the meter records and uses to determine the volume of gas flow.

Vortex meters are pretty similar to rotary gas meters. Unlike rotary meters, vortexmeters are used in industrial applications that require little custody transfer of gases.

Products and reference designs of Rotary gas meter

DC/DC power supply

Gas meters have digital, analog, and RF blocks with individual DC power requirements. Depending power levels TI has DC/DC converters, LDOs and power management ICs (PMIC) that can help to reduce power dissipation and size in the solution. DC/DC power supply includes Boost converters (integrated switch)、Buck converters (integrated switch)、Linear & low-dropout (LDO) regulators、USB power switches & charging port controllers、Buck-boost, inverting & split-rail converters (integrated switch)、Load switches、eFuses & hot swap controllers、Battery fuel gauges、P-channel MOSFETs、Precision ADCs、Analog current-sense amplifiers、General-purpose op amps, the corresponding products are TPS61322、TPS7A05、LM2776、TPS629210、TPS22919、CSD23280F3、BQ35100、OPA2310、ADS124S06

Metrology

The metrology subsystem of a water meter measures the volumetric flow of Water through the pipe. Electronic measurement of a rotating impeller can use different types of sensor technology including inductive, optical, and magnetic. Metrology includes MSP430 microcontrollers、Wi-Fi products、Linear & low-dropout (LDO) regulators、Series voltage references、Shunt voltage references、General-purpose op amps、Precision op amps (Vos<1mV)、Digital temperature sensors、Analog temperature sensors、ESD protection diodes, the corresponding products are MSP430G2855、CC3200、TPS782、REF35、LM4040、TLV9101、OPA2388、TMP119、LMT70A、TPD4S009

Application processor

Water meters require a host MCU to calculate the flow rate, to control the segment display, and to execute all required communications stacks. Low power consumption is a critical concern in this battery-powered application. Application processor includes MSP430 microcontrollers、Battery fuel gauges、P-channel MOSFETs、Brushed DC (BDC) motor drivers、General-purpose op amps、Noninverting buffers & drivers、NAND gates, the corresponding products are MSP430FR6922、BQ35100、CSD23280F3、DRV8850、TLV9102、SN74LVC1G17、SN74LVC00A

Wireless communication

Water meters use wireless communication to automatically report consumption data to the service operator. Low power consumption and RF sensitivity are important considerations. Wireless communication includes Sub-1 GHz wireless MCUs、Low-power 2.4-GHz products、Sub-1 GHz transceivers、Other wireless products、Wi-Fi products、MSP430 microcontrollers、General-purpose op amps、ESD protection diodes, the corresponding products are CC1314R10、CC2652R7、CC1120、RF430CL330H、CC3200、MSP430FW423、TLV9101、TPD4S009

Wired communication

Water meters use wired communication to automatically report consumption data to the service operator. MBUS is the most common wired communications standard in this industry. Wired communication includes RS-485 & RS-422 transceivers、ESD protection diodes、USB hubs & controllers、Linear & low-dropout (LDO) regulators、MSP430 microcontrollers, the corresponding products are THVD1500、TPD2E001、TUSB2046B、TPS782、MSP430FR6922

Anti-tamper

Water meters monitor for potential tampering for safety purposes and to assure accurate billing. Many different types of sensors can be used to detect tampering. Anti-tamper includes Inductive sensor AFEs、Battery fuel gauges, the corresponding products are LDC0851、BQ35100

Installation

To ensure optimal performance from any rotary gas meter, proper installation in accordance with the manufacturer’s recommendations is required. Rotary meters should be placed where they have the best chance of remaining uncontaminated for the best operation.

You can install the rotary gas meter by laying it either in the vertical or horizontal position. Before installing rotary gas meters, carry out the following pre-installation checks:

●Confirm the rotary piston meter is in perfect condition.

●Ensure the piping system of the gas meter is free from materials such as dirt and weld slag.

●Inspect the mounting flanges, ensuring they are parallel and well set apart.

●After performing a successful pre-installation check, install the meter using this procedure:

●Use the full flange gaskets.

●Tighten the flanges by using bolts and ensure you torque them using the correct value recommended by the manufacturer.

●Apply meter oil once done, as it will help with lubrication. Always use oil supplied by the manufacturing company to avoid damaging the impellers.

●Pressurize the installation at a slow rate of 35kPa per second until you achieve recommended pressure.

●Check for gas leaks.

Final Word – Why Choose a Rotary Gas Meter

Industry players prize the rotary gas meter for its high precision and ability to withstand extreme gas pressures and temperatures. These characteristics make them ideal for large, demanding industrial applications. In addition, rotary gas meters are an affordable measuring solution specifically for utility billing, submetering and custody transfer applications.

If you’re in the market for a rotary gas meter, Norgas carries Romet rotary gas meters which are among the most reliable measuring gas meters on the market. We have more than 34 years of experience in the gas supply industry, so we have the expertise to advise you on the right gas regulators and valves to match your rotary gas meter.