Rosemount 755, Instruction Manual

Page: 48 / 94

M
ODEL
755 O
XYGEN
A
NALYZER
3-8
748183-H Rosemount Analytical
November 1997
0 [100 + (-0.623 - (-0.358)] - 100 [-0.623 - (-0.358)]
100
= 0.265 % O
2
EXAMPLE: ZERO-SUPPRESSED RANGE
Range 50% to 100% oxygen
At lower range-limit, i.e., 50% oxygen composition of sample is: 50% oxygen:
30% CO
2
: 20% N
2
.
From Table 3-4, the % oxygen equivalents are: O
2
+ 100%, CO
2
, -0.623%; N
2
, -
0.358%
% oxygen equivalent of mixture
= 0.5 x (+100) + 0.3 x (-0.623) + 0.2 x (-0.358)
= +50.00 + (-0.187) + (-0.072)
= +49.7415% O
2
3.3.2 C
OMPUTING
A
DJUSTED
S
ETTINGS FOR
Z
ERO AND
S
PAN
C
ONTROLS
During instrument calibration, adjusted values may be required in setting the ZERO
and SPAN Controls, to correct for the magnetic susceptibility of the background gas.
The quantities are defined as follows (see Table 3-3):
BGGst = Oxygen equivalent of background gas in standard gas
BGGs = Oxygen equivalent of background gas in sample
PO = Operating pressure
Use the following equation to compute the adjusted settings for the ZERO and SPAN
Controls:
Adjusted % oxygen for standard gas =
[true % O
2
of standard gas] [100 + (BGGs - BGGst) ] - 100 [BGGs - BGGst]
100
Use the following equation to compute the adjusted settings for the ZERO and SPAN
Controls, see equation below.
EXAMPLE
Background gas in sample is CO
2
, oxygen equivalent = -0.623%.
Downscale standard gas is 100% N
2.
Upscale standard gas is air: 21% O
2
, 79% N
2
.
Background gas in downscale and upscale standard gases is N
2
, oxygen
equivalent = -0.358%.
With N
2
downscale standard gas flowing, ZERO control is adjusted so meter reads: