971B UniMag™
19
Operation manual
Pressure request:
Query: @253PR1?;FF
Query reply: @253ACK1.23E-4;FF
Pressure outputs:
PR1: Cold Cathode reading
PR2: Cold Cathode reading
PR3: Cold Cathode reading
PR5: Cold Cathode reading
The default analog output is based on the combined PR1 reading and provides a 16 bit voltage output of 0.5
VDC/decade standard configuration. Refer to Analog output page 25 for details.
If ionization does not ignite or if the cold cathode reading is lower than the cold
cathode zero value, the digital and analog output provides: 1.00E-8 Torr
When designing pressure data collecting software and controlling loop, make sure that the
software does not interpret a communication error as a valid pressure value.
Resolution
The digital pressure output can provide 3 digit or 4 digit values; however, the resolution is limited in certain
parts of the measuring range.
1.00E-7 to 1.00E-8 Torr
2 digits resolution
1.50E-8
5.00E-3 to 1.00E-7 Torr
3 digits resolution
1.230E-4
Measuring noise
External sources can interfere with the sensor signal and cause noise in the signal. The low measuring range
is most sensitive to measuring noise due to low signal levels.
Magnetic interference
External magnetic sources can interfere with the Cold Cathode sensor and cause measurement deviation
from actual pressure. Avoid having magnetic material located close to the 971B Transducer.
Cold Cathode ignition startup
When the Cold Cathode high voltage is enabled, an ignition delay may occur. The ignition waiting time is from
less than a second at high pressures to minutes at low pressures. The ignition time is a function of gas density
and cleanness of the gauge.
When the Cold Cathode is enabled, but ionization not ignited the LED will flash red. The LED will flash green
when valid measurements are present.
Pressure
Typical ignition time
1.00E-8 Torr
≈12 Minutes
1.00E-6 Torr
≈10 Seconds
1.00E-4 Torr
≈1 Second