Measurement Specialties 9116 - Manual (Page 100)

Pressure Systems, Inc. Model 9116 User’s Manual
Page 91 www.PressureSystems.com
Chapter 4
Calibration
4.1
Introduction
Each internal DH200 transducer in a Model 9116 Intelligent Pressure Scanner contains non-
volatile read/write memory capable of storing the transducer's full thermal and pressure
calibration data.
The Model 9116 Intelligent Pressure Scanner module uses a third-order polynomial to convert
transducer output voltage to pressure. All calculations are carried out internally using high
precision math. The following formula is used for all pressure output calculations.
P
T
(V) = [C
0
(T) + C
1
(T)*V + C
2
(T)*V 2 + C
3
(T)*V 3 ] * C
SPAN
- C
RZ
where:
P
T
= Calculated applied pressure
V = Transducer output voltage
C
0
(T) .. C
3
(T) = Conversion coefficients generated from calibration data at
temperature T.
C
RZ
= Re-zero adjustment’s “offset”correction coefficient
C
SPAN
= Span adjustment’s “gain” correction coefficient
Since the polynomial’s coefficients are a function of the current temperature, they are
dynamically re-calculated by the module firmware (with other equations) to compensate for each
transducer’s measured temperature change.
Each Model 9116 Intelligent Pressure Scanner contains an integral purge/leak check calibration
manifold. Through software commands, this valve may be placed in one of four positions: RUN,
CAL, PURGE, or LEAK-CHARGE. (See the Set/Do Operating Options/Functions (‘w’)
command (ii=0C & 12) in Chapter 3, and in particular the Valve Position Chart at the end of
command’s description.) When each module’s internal calibration valve is placed in the
CAL/RE-ZERO position (through software commands), all DH200 transducer pressure inputs
are pneumatically connected to the CAL input ports. All DH200 reference inputs are
pneumatically connected to the CAL REF input port. The CAL input may be used to perform
on-line zero adjustment of the 9116’s transducers. This capability virtually eliminates sensor
zero drift error and ensures the highest possible data accuracy. The CAL input may also be
used for DH200 span adjustment calibrations. Span calibration of multi-range scanners may
also utilize the CAL input ports if the highest applied pressure does not exceed the proof
pressure rating of any installed transducer.