MKS UniMag 971, Руководство по эксплуатации и установке, Страница: 19 / 44

971 UniMag ™ Operation manual 16
The 971 transducer can provide pressure measurement output as an analog voltage or RS232/RS485 digital
value. The digital value is 3 digits scientific notation for PR1, PR3, PR5 reading and 4 digits for PR4 reading.
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 21 for details.

If ionization do not ignite or if the cold cathode reading is lower than the cold cathode
zero value, the digital output provides: 1.00E-8 Torr
When designing external pressure control loops, make sure that external equipment like pumping
system is not damaged if the transducer output enters Sensor defect mode page 15 or in case of
power failure.
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 971 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.
The combined analog output and PR3, PR4 reading provides the MicroPirani reading until ignition has
occurred and valid Cold Cathode measurements is present. 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