Vacuum Transducers & Baratrons

Vacuum transducers and Baratrons are sensors that continuously monitor the Absolute pressure and deliver a millivolt (mV) or mill amp (mA) signal. Transducers generally refer to a sensing device that provides a continuous output, whereas sensors are devices that just detect the magnitude. In the current context of pressure monitoring, vacuum sensors detect the magnitude of absolute pressure. In contrast, vacuum transducers measure and provide a continuous electric output, directly proportional (linear correlation) to the changes in the magnitude of vacuum. Because of the constant analog output (generally in mV), vacuum transducers are widely used to automate control systems or interfacing pressure readings on an external analog display.

Types of Vacuum Transducers:

Based on the operational principle, vacuum (pressure) transducers are divided into two categories: direct (true) pressure monitoring devices (Ex: Baratrons) and in-direct pressure monitoring devices (Ex: Piezo, Pirani, etc.).

Direct (true) Pressure monitoring devices, as the name suggests, are transducers that detect true pressure (defined as the force per unit area) of an atmosphere, implying that the measurement is insensitive to the type of fluid to be monitored. Baratron Capacitance Manometers are the classic example of true pressure vacuum transducers. A Baratron sensor module contains a metal diaphragm (made of anti-corrosion alloy) connected to a metal-on-ceramic electrode structure. One side of the diaphragm (reference side) is evacuated to a very high vacuum (using internal chemical getter pumps), maintained at much lower pressures than that are to be measured. The other side (measuring side) of the diaphragm is connected to the volume to be monitored. The changes in capacitance between the metal diaphragm, caused by the diaphragm’s movement onto the adjacent, fixed dual-electrode, is measured to derive the true pressure magnitude. Most Baratrons have radially tensioned diaphragms to provide very low hysteresis and high resolutions. Because of the simplicity of the measuring principle, stand-alone Baratrons have excellent repeatability, high resolution (1×10-5 of Full Scale), fast response, and the ability to measure broad pressure ranges.

In-direct pressure monitoring devices, on the other hand, use multiple pressure measurement technologies such as  Pirani, Piezo (thermocouple), and ion gauges (Glass/Nude Bayard-Alpert Ionization), Hot and Cold cathode methods to determine the vacuum. These gauges do not measure the True vacuum pressure (force/area), and therefore, their readings will be gas-type sensitive.

Selection of Vacuum Transducers:

Depending on the application, range, and the accuracy of vacuum readings, the operational principle of vacuum gauge is selected. Following are the Vacuum transducer categories, grouped with their features:

1. Baratrons: Absolute Measurement Range – 0.1 to 1000 Torr. Direct pressure measurement, highly accurate and repeatable, insensitive to gas composition, compact and leakproof.
2. Pirani vacuum transducers: Absolute Measurement Range – 1×10-5 to 1000 Torr. Works on the principle of thermal conductivity using integrated Micro-Electro-Mechanical Systems. Robust transducers, resistant to damage from air inrush or vibration
3. Piezo vacuum transducers: Absolute Measurement Range – 1×10-1 to 1000 Torr. Works on the principle of metal sealed stainless steel diaphragm and integrated electronics. Economical, compact, and accurate can provide absolute pressure measurement (independent of gas type).
4. Cold cathode principle operating transducers: 1×10-8 to 0.005 Torr. Based on the cold cathode inverted magnetron sensor principle. Cost-effective solution for base pressure measurement and control with a broad pressure measurement range.
5. Micro Pirani or Piezo Loadlock: 1×10-5 to 1000 Torr. Works on the combination of Pirani and piezo principles. Used for fast, accurate, gas independent atmospheric measurement on load locks
6. Micro Ion transducers: Absolute Measurement Range – 1×10-9 to 1×10-2 Torr. Micro-Ion transducer provides high sensitivity for low noise & higher accuracy.

Applications:

1. Vacuum Transducers for differential pressure applications: Engine testing, fluid flow test stands, and wind tunnel simulations
2. Vacuum Transducers for absolute pressure applications: Weather stations, altimeter calibration equipment, and semiconductor fabs
3. Industrial applications: pump discharge pressure, fire hose discharge pressure, tank level, steam pressure in a boiler unit, food storage applications, etc.
4. Calibration and testing applications: Calibrating scientific instruments, cryogenic applications, and gauge testing

Vacuum Transducers Calibration – Why is it essential:

Vacuum transducers are precision Electro-Mechanical devices. Like any high tolerance device, temperature and other environmental factors impact the performance and accuracy of Vacuum transducers. Operators should therefore regularly monitor and eliminate the following errors, commonly detected in Baratrons and Vacuum transducers using calibration:

1. Zeroing errors: If the “zero” setting (reference setting) is altered, an offset or correction factor is induced across the entire range of the measurement.
2. Spanning errors: Span defines the instruments’ upper and lower limits of measuring range. When induced, these errors result in changing the overall measuring range of the transducer. It can be greater or smaller than the actual measuring span.
3. Linearity errors: Every transducer is prone to linearity errors. The endpoints (zero and full Scale) may be correct even when the transducer is out of adjustment, but the intermediate readings may be erroneous because of non-linear correlation.
4. Maintenance and external errors: Post calibration and zeroing, errors can occur due to a lack of operator expertise in handling precision equipment.

Cumulative defects in vacuum transducers often result in operational uncertainties leading to maintenance losses. Calibration avoids these errors, ensures Vacuum transducer’s accuracy for sustained and repeated use, and enhances their service life. Calibration frequency is primarily dependent on environmental conditions such as variations in the instrument’s physical orientation or ambient temperature. Following a regular and timely calibration schedule ensures accuracy of measurement and enhances process accuracy.

e2b calibration offers industry-leading ISO-certified Vacuum transducer and Baratron calibration services. Our labs are ISO/IEC 17025 accredited and operated by a team of qualified calibration experts to test and calibrate your Vacuum transducers. Our verifiable services are unmatched in the industry. We are registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We have the NIST Traceable Wide scope of ISO/IEC 17025 accreditation. Contact e2b calibration for all your equipment calibration needs.