INFICON HPG400 ATM to High-Vacuum Gauge - Manual (Page 25)

tina31e1 (2004-05) HPG400 v1.om
25
The measuring currents of the HP hot cathode and Pirani sensors are converted
into a frequency. A micro controller converts this frequency into a digital value rep-
resenting the measured total pressure. After further processing this value is avail-
able as analog measurement signal (0 … +10.2 V) at the output (sensor cable
connector Pin 2 and Pin 12) with the usable ranges 1.5 … 7.5 V (hot cathode) and
8.5 … 9.75 V (Pirani). The maximum output signal is internally limited to +10.2 V
(atmosphere). The measured value can be read as digital value through the
RS232C interface (Pins 13, 14, 15) (
→ 28). Gauges with a display show the
value as pressure. The default setting of the displayed pressure unit is mbar. It can
be modified via the RS232C interface (
→ 28).
In addition to converting the output signal, the micro controller's functions include
monitoring of the emission, calculation of the total pressure based on the meas-
urements of the two sensors, and communication via RS232C interface.
The HPG400 has five definable changeover thresholds (setpoint "emission on"). It
is thus possible to prevent the switching range from being situated within the proc-
ess pressure range. The factory setting of the threshold is 1 mbar. Other setpoints
can be selected via the <P
↔ HP> switch. Since the contamination of the hot
cathode system is reduced at low pressures, the lowest possible setpoint should be
selected.
Since the switch position is only polled upon activation of the gauge, the
setpoint should be selected before the gauge is turned on.
EMI ON
Hot cathode mode
Pirani mode
Switch position
<P
↔ HP>
Corresponding setpoint
0 or 1
2 or 3
4 or 5
6 or 7
8 or 9 1 mbar (factory setting)
5×10
–1
mbar
2×10
–1
mbar
1×10 –1 mbar
5×10
–2
mbar
The gauge is factory-calibrated. Adjustment may become necessary due to use in
different climatic conditions, extreme temperatures, contamination or aging
(
→ 37).
The accuracy is reduced in the pressure range above 1×10
-1
mbar and below
1×10 -5 mbar.
The output signal is gas type dependent. The characteristic curves (
→ Appendix A)
are accurate for dry air, N
2
and O
2
. They can be mathematically converted for other
gases (
→ Appendix B).
If you are using a INFICON vacuum gauge controller, you can enter a calibration
factor to correct the displayed measured value (
→ of the corresponding meas-
urement unit).
4.2 Operational Principle of
the Gauge
Selecting the
changeover threshold
Accuracy
Gas type dependence