Instruction Manual WGM701 Wasp
InstruTech
Page 3
1
Introduction / General Information
1.1
Description
The WGM701
Wasp™
vacuum gauge module combines
the
Cold Cathode
Inverted Magnetron technology with a
Pirani sensor to provide reliable and continuous pressure measurements from atmosphere to high vacuum.
A
cold cathode ionization gauge measures vacuum pressure by first ionizing gas molecules inside the vacuum
gauge and then measuring the resulting ion current. A large potential between the sensor anode and cathode
will cause ionization to occur. The amount of ion current generated from the ionized gas is proportional to the
pressure in the vacuum system and is dependent on the type of gas used. As the pressure inside the vacuum
system drops, the measured ion current drops. Two ion current collector options are available. The low current
collector option is recommended for use in heavy gases such as argon to prevent self-sputtering while the high
current version is recommended for gases such as N
2
/air, etc. The Pirani sensor measures pressure indirectly by
sensing the loss of heat from a sensor to the surrounding gases. The higher the pressure of the surrounding gas,
the more heat is conducted away from the sensor. Pirani thermal conductivity gauges maintain a sensor (usually
a wire) at some constant temperature, and measure the current or power required to maintain that
temperature.
The WGM701 provides the basic signal conditioning required to turn the sensor into a complete vacuum
pressure measurement instrument. The built-in controller provides a log-linear analog output for the measured
pressure. The cold cathode sensor is automatically activated once the pressure measured by the Pirani sensor
has indicated a low enough pressure level of 7.6 x 10
-3
Torr.
Additionally, the instrument provides a sensor
on/off status using an open collector transistor output as well as several status LEDs. The measurement range
for the WGM701 cold cathode Pirani combination gauge is 7.6 x 10
-10
to 760 Torr.
1.2
Specifications
measurement range
7.6 x 10
-10
to 760 Torr / 1 x 10
-9
to 1,000 mbar / 1 x 10
-7
Pa to 101 kPa
accuracy - N2 (typical)
7.6 x 10
-9
to 7.6 x 10
-3
Torr: ± 30% of reading
7.6 x 10
-3
to 75 Torr: ± 15% of reading
75 to 760 Torr: ± 50 % of reading
repeatability - (typical)
7.6 x 10
-9
to 75 Torr: ± 5% of reading
materials exposed to gases
pirani sensor: tungsten cold cathode anode: molybdenum
others: Ni alloy, AI
2
O
3
, stainless steel, glass
internal gauge volume
1.391 in3 (22.8 cm3)
admissible pressure
145 psi, 10 bar absolute (limited to inert gases < 50
o
C)
temperature
operating: + 5 to + 55
o
C storage: -40 to + 70
o
C
humidity (30 days a year)
7.6×10-
8 … 7.6 ×10
-3 Torr 0 to 95% relative humidity, non-condensing
7.6×10-
9 … 7.6 ×10
-3 Torr 0 to 70% relative humidity, non-condensing
bakeout temperature (at flange)
150
o
C (sensor only - electronics removed)
weight
0.61 lb. (0.28 kg) with NW25 KF flange
housing (electronics)
aluminum extrusion
use
indoor only
mounting orientation
any
analog output
log-linear 0.5 to 7 Vdc, 0.5 V/decade
