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Model 2002 page 17
Rear Panel Description
SECTION 4
A schematic of the rear panel of the Model 2002 control unit is shown in Figure 4.2 ( Rear Panel Figure).
The transducer is connected to the control unit via an female 9-pin “D” connector on the rear panel. An
I/O cable can be connected via a male 9-pin “D” connector on the rear panel. The I/O cable provides an
analog output signal, a remote zero input capability, high and low alarm TTL outputs, and a + 5 VDC
Power Supply Output. The I/O cable also provides an analog ground and a digital common.
4.1 Remote Zero Input
The Model 2002 can be zeroed remotely via the I/O cable using the remote zero input line. Upon setting
this line to TTL low level, the instrument will set its current pressure reading to zero. A common applica-
tion of this feature is to utilize a process control output from a high vacuum gauge (for example an ion
gauge controller) to automatically zero the Model 2002 whenever the pressure is below the low 10
-5
To r r
range. A Digital Common is provided on pin # 5 which can be used with relay contacts or switch
contacts to remotely zero the instrument.
4.2 Analog Output
The Model 2002 provides an analog voltage output signal (0.5 VDC linear per decade) for process
control and for pressure monitoring. A plot of the analog output signal as a function of pressure is
shown in Figure 4.1 . Note that the output voltage is directly proportional to the pressure over each
complete decade (see detailed region in Figure 4.1) and that each decade has a different linear slope.
Above an indicated pressure of 10
3
Torr, the analog output signal will be +5 VDC. Below the minimal
displayable pressure of 1 x 10
-4
Torr, the analog output will be 1.0 VDC.
V =
(EXP + 6) (MANT - 1)
218
+
The analog output voltage is given by the following equation:
Where EXP is equal to the exponent of the displayed pressure.
EXP = -2
MANT = 1.53
V =
=
=
2 + 0.0294
2.0294 VDC
(-2 + 6)
2
(1.53 - 1)
18
+
example: p = 1.53 x 10
-2
EXP = +2
MANT = 9.87
V =
=
=
4 + 0.4928
4.4928 VDC
(+2 + 6)
2
(9.87 - 1)
18
+