Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 72)

FAQ Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 54
5.4. Calibration Valves Options
There are four available options involving Zero/span valves. From an operational and software
standpoint, all of the options are the same, only the source of the span and zero gases are different.
5.4.1. Ambient Zero/Pressurized Span Valve
This option requires that both zero air and span gas be supplied from external sources. It is specifically
designed for applications where span gas will be supplied from a pressurized bottle of calibrated CO
2
gas.
A critical flow control orifice, internal to the instrument ensures that the proper flow rate is maintained. An
internal vent line, isolated by a shutoff valve ensures that the gas pressure of the span gas is reduced to
ambient atmospheric pressure. Normally zero air would be supplied from zero air modules such as a
Teledyne Instruments Model 701.
In order to ensure that span gas does not migrate backwards through the vent line and alter the
concentration of the span gas, a gas line not less than 2 meters in length should be attached to the vent
span outlet on the rear panel of the analyzer. To prevent the buildup of back pressure, this vent line
should not be greater than 10 meters in length.
The following table describes the state of each valve during the analyzer’s various operational modes.
Table 5-1: Ambient Zero/Pressurized Span Valve Operating States
MODE VALVE CONDITION
SAMPLE
(Normal State)
Sample/Cal Open to SAMPLE inlet
Zero/Span Open to IZS inlet
Shutoff Valve Closed
ZERO CAL
Sample/Cal Open to ZERO/SPAN valve
Zero/Span Open to IZS inlet
Shutoff Valve Closed
SPAN CAL
Sample/Cal Open to ZERO/SPAN valve
Zero/Span Open to SHUTOFF valve
Shutoff Valve Open to PRESSURE SPAN Inlet
The minimum span gas flow rate required for this option is 800 cm 3 /min.
The state of the zero/span valves can also be controlled:
 Manually from the analyzer’s front panel by using the SIGNAL I/O controls located under the DIAG
Menu (Section 6.13.2),
 By activating the instrument’s AutoCal feature (Section 7.6),
 Remotely by using the external digital control inputs (Section 6.15.1.2 and Section 7.5.2), or;
 Remotely through the RS-232/485 serial I/O ports (see Appendix A-6 for the appropriate commands).