Instruction Manual VGC301A Controller
InstruTech, Inc.
Page 21
7
Analog Output
The VGC301 provides either a non-linear, log-linear or a
0-10 Vdc linear analog output signal.
Non-Linear Output
The first Convectron
®
gauge controllers produced a non-linear
output signal of 0.375 to 5.659 Vdc for 0 to 1000 Torr of N
2
,
roughly in the shape of an "S" curve, as shown at right.
Granville-Phillips
®
adopted the same output curve for most of
their Mini-Convectron
®
modules and controllers with non-linear
output (although in recent years, some Granville- Phillips
®
controllers may output variations of the original S-curve).
The non-linear output from InstruTech convection gauges,
modules, and controllers duplicates the original S-curve of
0.375 to 5.659 Vdc for 0 to 1000 Torr.
The tables shown in section 7.1 and 7.2 contain the lookup data
for converting the non-linear output voltage into pressure
values for nitrogen and various other gases.
Log-Linear Output
Many InstruTech modules and controllers also provide a log-
linear output signal, as an alternative to the non-linear signal
described above. This output, shown at right, is a 1 Volt per
decade signal that may be easier to use for data logging or
control.
The tables shown in section 7.3 and 7.4 contain the lookup data
and provides the formulas for converting the log-linear output
voltage into pressure values for nitrogen and various other
gases.
Linear 0-10 Vdc Analog Output
The VGC301 also provides a linear 0-10 Vdc analog output. The linear output voltage can be any value between 10
mV and 10 V corresponding to displayed pressure between 1 mTorr and 1000 Torr. However, the useful range of the
linear analog output is three decades. For example if the minimum pressure selected is 1 mTorr (1.0 x 10
-3
Torr) with
a corresponding minimum voltage output of 0.01 volts, then maximum pressure selected to correspond to a
maximum voltage output of 10 volts should not exceed 1.0 Torr. If your application requires the analog output to
cover a pressure range exceeding three decades then consider using the non-linear or the log-linear analog output.
Note that an analog output of less than 0.01 volts (to near 0 volt) may indicate a damaged or faulty sensor.
Non-Linear Analog Output
10
+3
10
-3
10
-2
10
-1
10
0
10
+1
10
+2
1
2
3
4
5
6
Pressure - Torr
Output - Volts
Non-Linear Analog Output
10
+3
10
-3
10
-2
10
-1
10
0
10
+1
10
+2
1
2
3
4
5
6
Pressure - Torr
Output - Volts
10
+3
10
-3
10
-2
10
-1
10
0
10
+1
10
+2
1
2
3
4
5
6
Pressure - Torr
Output - Volts
10
+3
10
-3
10
-2
10
-1
10
0
10
+1
10
+2
2
3
4
5
6
7
8
Pressure - Torr
Output - Volts
Log-Linear Analog Output
1
10
+3
10
-3
10
-2
10
-1
10
0
10
+1
10
+2
2
3
4
5
6
7
8
Pressure - Torr
Output - Volts
Log-Linear Analog Output
1