Model 755R

Instruction Manual

748213-S April 2002

Use the following equation to compute the adjusted settings for the ZERO and SPAN controls:

Adjusted % O2 for standard gas =

(A)[100 + (B-C)] - 100 [B-C]

100

Where:

A= true % O2 of standard gas

B= BGGs

C= BGGst

Example:

Background gas in sample is CO2, oxygen equivalent = -0.623% Zero gas is 100% N2

Span standard gas is air: 21% O2, 79% N2

Background gas in zero and span standard gases is N2, oxygen equivalent = -0.358% With N2 zero standard gas flowing, ZERO control is adjusted so digital display reads:

0[100+(-0.623-(-0.358))] - 100[-0.623-(-0.358)]

100

= 0.265% O2

With air flowing, SPAN control is adjusted so the digital display reads:

21[100 - 0.265) - 100 (-0.265)

100

= 21.209% O2 ≅ 21.21

In two limiting cases, the general equation is reduced to simpler forms.

1.If the span standard gas is 100% oxygen, the adjusted oxygen value for setting the SPAN control is the same as the true value (i.e., 100% oxygen).

2.If the zero standard is an oxygen-free zero gas, the adjusted value for setting the ZERO control = BGGst - BGGs. (If the oxygen-free zero gas is more diamagnetic than the background gas in the sample, this difference is negative. The negative value may be set on the digital display or the re- corder if provided with below-zero capability.)

Rosemount Analytical Inc. A Division of Emerson Process Management

Operation

3-5