Teledyne 2120 - Trace Nitrogen in Argon Analyzer - Manual (Page 41)

Trace Nitrogen in Argon Analyzer Operation
4.2 Zero and Span Calibration
The Model 2120 is designed to provide a linear response over the
0-20/0-200 or the 0-2/0-20 ppm concentration range for nitrogen in
argon. Therefore, a two-point (zero and span) calibration is sufficient to
define the calibration curve for this analyzer.
Prior to shipment, the analyzer was calibrated by the factory in
accordance with the calibration data shipped with your analyzer. Use
these settings to verify that the unit is in calibration, or re-calibrate the
analyzer as outlined in this section.
4.2.1 Before Calibration
Note: To minimize consumption of zero and span gases, careful
attention to the purging of the analyzer, as described in
Chapter 3, is critical.
1. Ensure that the analyzer is fully purged and warmed up.
2. Check to make sure that the low flow light is not illuminated.
3. Check that the sample gas flow rate is 2 cfh (940 ccpm), as
indicated on the front panel flowmeter. Adjust sample flow by
adjusting the pressure regulator on the sample inlet. Do not
exceed a maximum of 7 psig (76 kPa).
4.2.2 Recommended Calibration Gases
Teledyne recommends the following gases be used for calibration:
For 0-2 ppm range: zero gas—N
2
-free Ar
span gas—1.60 – 2 ppm N
2
in Ar
For 0-20 ppm range: zero gas—0 – 2 ppm N
2
in Ar or N
2
-free Ar
span gas—16 – 20 ppm N
2
in Ar
For 0-200 ppm range: zero gas—0 – 2 ppm N
2
in Ar or N
2
-free Ar
span gas—160 – 200 ppm N
2
in Ar
The first calibration point is fixed by a zero gas. The most
convenient source of nitrogen-free argon is through an activated
molecular sieve getter cooled to liquid oxygen temperatures or a heated
transition metal getter. A commercially available instrument, the GOW-
MAC® Model 75-800 Noble Gas Purifier, is ideal for this. A zero gas
Teledyne Analytical Instruments
31