Chemglass AF-0304 - Manual (Page 16)

4.4.1 Optional 4-20 mA and 0-5 or 0-10 VDC Output
Gauges provided with an optional output are built in 1/4
DIN size cabinets which mount in 92 mm square panel
cut-outs.
On the rear panel of the instrument you will find a section
identified as “analog output” which includes the zero
and span adjustment potentiometers and a male connec-
tor for the 4-20 mA, 0-5 or 0-10 VDC outputs.
Unplug this connector and unscrew the gray plastic
shroud. Feed a shielded wire through this shroud and
solder the shield to the outside lug and the center con-
ductor to the inner lug. The shield is the circuit common
or zero and the center conductor is 20 mA, 5 or 10 volts.
The output is floating. The resistance in the mA output
loop can be up to 1000 ohms. The 5 or 10 VDC output
should have loads of 2000 ohms or higher.
Before being shipped from the factory the 4 mA is scaled
to the low end of the instrument range (or zero pressure)
and the 20 mA is adjusted to coincide with the full scale
instrument reading of 100mT, 2000mT, 20.00 Torr or
1500 Torr. Instruments built with 5 or 10 VDC outputs
are also scaled before shipping. Rear panel zero and
span adjustments are provided with all output ranges
should fine tuning in the field be required.
The standard analog output voltage signal described in
section 4.4 of the manual continues to function even
when these optional outputs are provided.
4.5. Calibration
There are only 3 calibration adjustments that are normally
necessary to re-standardize the instrument. One is an
offset adjustment. The other two amount to a “zero”
adjustment for hard vacuum, and a span adjustment to
set up scale tracking at some known pressure. There are
two methods for setting these adjustments. The methods
are described in the following two sections.
14