Bourdon Gauge
Deflection gauges measure true pressure via deflection of a bourdon tube, independent of the type of gas in a system. Bourdon tubes are constructed in either C-tube or helical coil geometries and of these two, helical Bourdon tubes provide the greatest sensitivity. 

MDC Bourdon gauges are designed for rough vacuum measurements in the range of 30 inches of mercury and positive pressures to 30psig. As a general rule, all vacuum components and chambers are rated for vacuum service and should never be internally pressurized. Bourdon gauges are offered with Del-Seal™ CF metal seal flanges, Kwik-Flange™ ISO KF flanges and male NPT pipe thread fittings. 

Thermocouple Gauge Tube
MDC thermocouple gauge tubes offer fast and reliable vacuum measurement from 1 to 1x10-4 Torr.

Thermocouple gauge tubes consist of two basic components, a resistive filament and a thermocouple junction used to measure its temperature. Thermocouple gauge tubes operate on the thermal conductivity principle. Basically, they measure the thermal conductivity of a residual gas inside a vacuum system, or its ability to conduct heat away from a heated filament. 

The higher the pressure inside a vacuum system the cooler the filament or conversely, the lower the gas pressure the hotter the filament becomes.The thermocouple junction inside the gauge tube is positioned on the heated filament and is used to monitor its temperature during system evacuation. A temperature rise or drop in the filament produces a potential rise or drop in the thermocouple junction. This potential in millivolts, is then calibrated to microns in a thermocouple gauge controller. 

Because thermocouple gauge tubes and control electronics are available from a multitude of manufacturers, it is important to note that individual thermocouple gauge tubes are designed to operate at specific filament current ratings, which should be carefully matched with a control instrument’s specifications. Always refer to the control electronics manufacturer for specifications on filament current requirements before purchasing or installing a thermocouple gauge tube.

MDC UHV gauge tubes feature all-welded construction and stainless steel casing tubes that are bakeable to 150°C. Electrical connections are glass insulated and employ a standard eight pin interface with a polarized center post. They are offered with Del-Seal™ CF flanges and Swagelok’s VCR® fittings. HV gauge tubes are supplied with male NPT pipe thread fittings and a nickel plated steel shell assembly for maximum corrosion resistance and bakeable to 150°C.

Thermocouple gauge tubes are expendable vacuum components and must be replaced periodically. Most gauges are typically calibrated for service in air (nitrogen) and experience extreme variations in calibration when in the presence of other gases, subsequently leading to erroneous vacuum measurement readings. An inexpensive solution would be to include a non-gas-dependent gauge such as a Bourdon gauge to verify calibration.


Glass Enclosed Ionization Gauge Tube
MDC glass enclosed ionization gauge tubes are designed for high and ultrahigh vacuum measurements between 1x10-3 to 2x10-10 Torr. Glass enclosed ionization tubes, commonly referred to as a Bayard-Alpert gauge tubes, consist of several components including a resistive filament, a positively charged grid and a negatively charged collector. The resistive filament is heated to incandescence for the purpose of emitting electrons. The grid, a positively charged wire, coiled in the shape of a spiral, attracts
and accelerates filament emitted electrons. The collector, a negatively charged wire, is strategically placed in the path of oncoming electrons. As electrons collide with air molecules inside the tube, the air molecules lose an electron and become positively charged or ionized and thus attracted to the negatively charged collector. Upon colliding with the collector air molecules regain their lost electron and return to their original neutral charge. The flow of electrons from the collector to air molecules is measured and calibrated for vacuum measurement. The number of air molecules is directly proportional to their ionization and in direct proportion to the flow of electrons surrendered by the collector.

Nude Ionization Gauge Tube
MDC nude ionization gauge tubes are designed for high and ultrahigh vacuum measurements between 1x10-3 to 2x10-11 Torr. Like their glass enclosed counterparts, these are also hot cathode ionization types. The main difference being their method of construction. Nude gauges allow for easy replacement of perishable filaments and the added durability of ceramic-to-metal electrical feedthrough insulation which makes them bakeable to 450°C. Two nude gauge styles are offered, these are resistive heating or electron bombardment degas.