Instruction Manual
748213-S
April 2002
Rosemount Analytical Inc. A Division of Emerson Process Management Operation 3-5
Model 755R
Use the following equation to compute the adjusted settings for the ZERO and SPAN controls:
Adjusted % O
2
for standard gas =
Where:
A = true % O
2
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:
With air flowing, SPAN control is adjusted so the digital display reads:
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.)
0[100+(-0.623-(-0.358))] - 100[-0.623-(-0.358)]
100
=
0.265% O
2
21[100 - 0.265) - 100 (-0.265)
100
= 21.209% O
2
≅
21.21
(A)[100 + (B-C)] - 100 [B-C]
100
