MKS 979B Atmosphere to Vacuum Transducer

GC (gas correction) query/set gas correction coefficient for hot cathode (0.10-50.1, default 1, such as argon 1.29) setting: @ 001GC! 1.29; FF

Analog output and gas correction

1. Simulation output calculation and table

DAC1: Pressure calculation formula P=10 (2V − 11) (Torr), the manual provides a detailed voltage correspondence table for 1.0E-10 Torr (0.50V) to 1.0E+03 Torr (7.00V).

DAC2: Pressure calculation formula P=10 0.75 V − 7.75 (Torr), also provide a complete pressure voltage correspondence table.

2. Gas correction factor

MicroPirani is based on gas thermal conductivity measurement, and the hot cathode is based on gas ionization measurement, both of which need to be corrected according to the gas type:

Gas chemical formula gas correction factor (GC)

Air -1.00

Argon gas Ar 1.29

Carbon dioxide CO ₂ 1.24

Deuterium gas D ₂ 0.35

Helium He 0.18

Hydrogen H ₂ 0.46

Krypton gas Kr 1.94

Neon gas Ne 0.30

Nitrogen N ₂ 1.00

Nitric oxide NO 1.16

Oxygen O ₂ 1.01

Sulfur hexafluoride SF ₆ 2.50

Water H ₂ O 1.12

Xenon Xe 2.87

Maintenance and troubleshooting

1. Daily maintenance

Cleaning: The casing can be cleaned with water or alcohol to prevent liquids from entering the electronic casing; The sensor tube must not be cleaned (as it may damage the components), and the sensor needs to be replaced in case of severe contamination.

Degassing operation: When the hot cathode sensor is contaminated by process gas (especially when the sensitivity drifts when the pressure is ≤ 10 ⁻⁸ Torr), regular degassing is required; When degassing, the pressure should be less than 1 × 10 ⁻⁵ Torr. During this period, the pressure can be measured but the reading may be higher than the system pressure. When the pressure is greater than 1 × 10 ⁻⁴ Torr, degassing is paused and restarted after reaching the threshold. It will automatically terminate after 30 minutes, and degassing should not exceed 30 minutes every 4 hours.

2. Common faults and solutions

Possible causes/solutions for the fault phenomenon

RS-485/RS-232 no response 1. Missing starting character @; 2. Address error (you can try @ 254; FF query); 3. Missing termination character; FF; 4. Baud rate mismatch; 5. Missing/incorrect electrical connections

MicroPirani reading too high/too low/