Delta NANOTRACE DF-745 Instruction Manual download pdf (Page 73)

Sample Gas Preparation and Delivery DF-745 69

8 Sample Gas Preparation and

Delivery

8.1 Introduction

It is important to note key differences in each parameter to ensure a properly functioning

system. Parameters such as flow, pressure, and background gas will have major effects on

total system performance.

8.2 Sample Flow Rate and Pressure

Proper moisture analyzer operation is dependant upon the pressure of the sample gas. For

each sample gas, there is a unique pressure range that the analyzer must operate under. See

Table 7 for the proper settings. Proper analyzer operation is contingent upon maintaining

the sample pressure for a given background gas within this range. The pressure can be

adjusted by balancing the inlet regulator setting with the throttling valve in the aspirator or,

if equipped, with the needle valve in the vacuum pump assembly.

Background Gas

Pressure

200 +/

20 Torr

330 +/

20 Torr

780 +/

20 Torr

350 +/

20 Torr

350 +/

20 Torr

Table 7: Sample Outlet Pressure

8.3 Flow Rate Effects on Sensor Performance

Assuming a leak-free system, flow rate changes will have minimal effects on the

performance of the moisture cell.

8.4 Sample Gas Scale Factor

8.4.1 Background Gas Effects on Indicated Flow Rate

If the molecular weight of the background gas is much different from N

, the flowmeter

reading is not accurate. The bypass loop flowmeter mounted on the rear of the DF-700

series Moisture Analyzer is calibrated for use in air (or N

). Most other gases have

molecular weights within ± 25 percent of air. Since the required flow rate is not extremely

critical most gases produces reasonably correct readings. The exceptions are light gases

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Delta NANOTRACE DF-745 Instruction Manual Page 73