3-8 / Calibration
2808B
Suppressed Zero Calibration
:
0 psi < 1V (4-20mA) output [0 psi results in an output less than 1V (4mA)]
Sample
Ranges:
1 to 10 psi
10 to 60 psi
50 to 100 psi
The above procedures are described in topics 3.6, 3.7, and 3.8. Select the procedure you
require.
3.6 ZERO-BASED CALIBRATION
This procedure describes the process by which the zero and span settings are obtained for
the 1-5V and 4-20mA output stages of the 2808 DP and PT transmitters.
The following parameters relate directly to the calibration process:
URL
:
Upper Range Limit of sensing element. The URL is the maximum input
pressure that can be applied without over-pressuring the sensing
element.
Span
:
The algebraic difference between the limits of the range (P
max
– P
min
).
The desired span must always be less than or equal to the upper range
limit (URL) of the sensing element. Span is expressed as a percentage of
the upper range limit of the sensing element.
Zero
:
The point within the available pressure range the user defines as a zero
pressure reference.
P
max
:
Maximum input pressure of a desired range, not necessarily the
maximum range of the sensing unit.
P
min
:
Minimum input pressure of a desired range.
Theory of Operation
: The output stage can potentially take a user defined portion of the 0-
100% URL pressure input, and display it as a corresponding 1-5V or 4-20mA output. The
range, desired by the user, is obtained by setting the appropriate coarse and fine zero and
span settings. Each coarse setting is described in Tables 3-A and 3-B, whereas the fine
settings are adjusted manually until the desired output is achieved. Fine adjustments are
made with two external adjustment screws. The output stage is designed to yield a Turn
Down of better than 6, while the fine adjustment screws should affect the output zero and
span by no more than 1.5%/Turn.
3.7 ELEVATED ZERO CALIBRATION
1.
Calculate the total span required for the elevated zero range. For example, if the desired
elevated zero range is -10 to +30 psi, the total span will be 30-(-10) = 40 psi.
Summary of Contents for Bristol 2808 Series
Page 12: ...BLANK PAGE ...
Page 14: ...1 2 Introduction 2808B Figure 1 1 2808 XXB Transmitters ...
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Page 32: ...1B 2 DP Transmitters 2808B Figure 1B 1 Model 2808 35B Figure 1B 2 Transmitter Assemblies ...
Page 40: ...1B 10 DP Transmitters 2808B Figure 1B 6 Transmitter Housing Rotation Diagram ...
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Page 57: ...2808B Calibration 3 3 Figure 3 2 Calibration Adjustments ...
Page 60: ...3 6 Calibration 2808B TABLE 3 A COARSE ZERO SWITCH SETTINGS Elevation ...
Page 61: ...2808B Calibration 3 7 TABLE 3 B COARSE ZERO SWITCH SETTINGS Suppression ...
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Page 68: ...4 2 Service 2808B Figure 4 1 Using Internal TEST Terminals to Measure Current ...
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