CVM201 FAQ

What is the principle of operation?
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Click image to enlarge

A convection enhanced Pirani vacuum gauge is a thermal conductivity gauge which measures pressure by sensing the loss of heat from a sensor wire to the surrounding gases. There are several physical effects that remove heat from the sensor. First, heat is removed from the sensor wire through the ends of the wire suspended in the vacuum region by the relatively large mass of the supports that attach the wire to the hermetically sealed electrical connections. Second, heat is removed from the suspended wire via conduction to the gas inside the transducer volume. Heat is also lost from the sensor by thermal radiation. Finally, for the convection enhanced Pirani-type transducer, heat transfer from the sensor is aided by convection currents of the gas at higher pressures inside the transducer volume.

The convection enhanced Pirani gauge operates by maintaining a sensor wire at some constant temperature, and measuring the power required to maintain that temperature. If convection currents, gas conduction, thermal radiation and end-loss heat transfer characteristics are constant, a constant power level delivered to the sensor wire will keep the wire at a constant temperature. If any of the physical effects change, the wire temperature will change. For example if the gas density and pressure around the wire is decreased, the wire will get hotter. If the gas density and pressure around the wire is increased, the wire will be cooled. By monitoring the amount of power required to the keep the sensor wire at a constant temperature, the pressure of the gas can be determined.
What is the measurement range of the CVM201?
1.00E-04 to 1,000 Torr
1.30E-04 to 1,333 mbar
1.30E-02 Pa to 133 kPa
Why is the CVM201 referred to as a “Module”?
Module is a complete vacuum gauge which combines the sensor and electronics (controller) in one assembly requiring no external controller to operate. The CVM201 is a vacuum gauge module with a built-in controller, display and it also provides process control signals.
What is the difference between a Convection Enhanced Pirani and a conventional Pirani gauge?
They are both considered thermal conductivity gauges. The convection gauge however utilizes the effect of heat-loss aided by convection cooling to extend the useful measurement range beyond that of the conventional Pirani transducer. Most Pirani vacuum gauge transducers have a useful measurement range of about 1.00E-04 to 1 or 2 torr. Convection Enhanced Pirani-type gauge such as the CVM201 extends the measurement range from 1.00E-04 to 1000 torr.
What is the power requirement of the CVM201?
11 to 28 Vdc, 2 W. Users can provide their own power supply or use InstruTech’s optional power supply PS401-A.
Can the CVM201 operate on batteries?
Yes but due to the power draw conventional batteries will not last for an extended period of time. InstruTech offers the optional PS402-A battery pack that uses two replaceable 9 V batteries and can provide 3 to 6 hours of continuous operation. For continuous operation consider using the PS401-A power supply instead.
What are the available output signals from the CVM201?
2 analog outputs, 2 setpoint relays and RS232 / RS485 serial communications.
What is the difference between the CVM201 and CVM211?
They are both vacuum gauge modules with built-in displays and use the same type of convection enhanced Pirani sensor. The difference is in the type and number of electrical signals provided. The CVM201 provides 2 analog outputs, 2 setpoint relays and RS232 / RS485 serial communications. The CVM211 provide 1 analog output and 1 setpoint relay.
What is the difference between the CVM201 and CVG101?
CVM201 is a vacuum gauge module with a built-in controller and display requiring no other controller to operate. The CVG101 is a vacuum gauge sensor which requires an external controller to operate.
Can the CVM201 be installed in any orientation?
Mount the convection gauge with its main (long) axis horizontal. Pressure reading errors may occur above 1 Torr if the unit is not mounted horizontally. Below 1 Torr, mounting position has little to no effect.
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