Pressure Systems 98RK-1 user manual Chapter Calibration 4.1 Introduction, Cspan

Pressure Systems, Inc. 98RK-1 & 9816 User’s Manual©

Chapter 4

Calibration

4.1Introduction

Each individual DH200 transducer within the NetScanner™ System Intelligent Pressure Scanner contains nonvolatile read/write memory capable of storing the transducer’s full thermal and pressure calibration data. The internal firmware of each module reads all of these calibration data from each transducer upon power up and then dynamically calculates 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.

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.

PT(V)	=	[C0(T) + C1(T)*V + C2(T)*V2 + C3(T)*V3] * C SPAN + CRZ
where:
PT	=	Calculated applied pressure
V	=	Transducer output voltage
C0(T) .. C3(T)	=	Conversion coefficients generated from calibration data at
CRZ		temperature T.
	=	Re-zero adjustment’s “offset" correction coefficient
CSPAN	=	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 9816 Intelligent Pressure Scanner contains an integral purge/leak check calibration manifold. Through software commands to each 9816, 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.) The 98RK-1 contains pneumatic backplane inputs for CAL (CAL 1-8)and CAL REF. When each module’s internal calibration valve is placed in the CAL/RE-ZEROposition (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 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 1-8ports if the highest applied pressure does not exceed the proof pressure rating of any installed transducer.

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