Teledyne HASTINGS 2002, Инструкция по эксплуатации, Страница: 15 / 49

page 15
Rear Panel Description
SECTION 4
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 high level (+ 5 VDC), the instrument will set its current pressure reading to
zero. A common application 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
-6
Torr range. A +5 VDC TTL level is provided on
pin # 7 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 4.2 (analog out figure). 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
4
Torr, the analog output signal will
be + 5 VDC. Below the minimum displayable pressure of 1x10
-4
Torr, the analog output will be 1.22
VDC. The output voltage corresponds to the following formula where Exp is equal to the expo-
nent of the displayed pressure and Mant is equal to the mantissa. V is equal to the analog output
voltage.
V = (Exp+6)*0.5 + (Mant - 1.0)/18
If the analog output is being used in a data acquisition system the following formulas can be used to
map the analog voltage into the measured pressure.
Exp = Int(2*V)-6
Mant = 18*{V-[(Exp +6)/2]}+1
Pressure = Mant*10
Exp
Where Int stands for a conversion to integer by truncation.
4.3 TTL Outputs
TTL outputs are provided for process control. High and Low set points are entered on the front
panel (see Section 3.4) and TTL signals are generated on the I/O cable in the following manner:
1) When the pressure as indicated by the Model 2002 is above the high set point, the high signal
line (pin #3) will be set to a TTL high level (+5 VDC). When the indicated pressure is below
the high set point, the high signal line (pin#3) will be set to a TTL low level (+0 VDC).
2) When the pressure as indicated by the Model 2002 is below the low set point, the low signal
line (pin #4) will be set to a TTL high level (+5 VDC). When the indicated pressure is above
the low set point, the low signal line (pin #4) will be set to a TTL low level (+0 VDC).
These TTL signals are used for a variety of applications. With these signals, the user has the
capability to turn off/on various equipment such as valves, flow controllers, pumps, heaters, and
safety equipment.