Pressure Systems 9022 - Manual (Page 111)

Pressure Systems, Inc. NetScanner™ System (9016, 9021, & 9022) User’s Manual
www.PressureSystems.com 4 - 1
Chapter 4
Calibration
4.1 Introduction
Each internal DH200 transducer in a NetScanner ™ System Intelligent Pressure Scanner (Model
9016) contains non-volatile read/write memory capable of storing the transducer's full thermal and
pressure calibration data. For Models 9021 and 9022, most Series 9400 transducers (that have
“digital compensation” specified for them) also have thermal sensors and on-board non-volatile
memory. However, 9400 and 9401 transducers with ranges greater than 750 psi, all 9402 transducers,
and other analog only transducers do not contain storage or thermal sensors. These units are
generally measured as scaled voltages only. The internal firmware of each module reads all of the
calibration data in any available memory from each transducer upon power up and then dynamically
calculates other conversion coefficients that convert transducer output into pressure at the current
measured temperature. The firmware uses these coefficients for all subsequent engineering-unit data
conversions performed. If no memory is found, that channel reads voltage (NOT EU pressure). In
this case, any command responses or streams that normally return pressure values return voltage
values instead.
All NetScanner ™ System Intelligent Pressure Scanner modules use 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.