Measurement Specialties 9116 - Manual (Page 102)

Pressure Systems, Inc. Model 9116 User’s Manual
Page 93 www.PressureSystems.com
4.2 Re-zero Calibration
All Model 9116 Intelligent Pressure Scanners are capable of independently performing a
transducer calibration adjustment function, referred to as Re-zero adjustment (or simply Re-zero
Cal). The Re-zero calibration will result in a recalculated “offset” coefficient for each channel
being calibrated, which automatically compensates for any transducer offset drift errors. Since
the factory-set coefficients in each transducer (that characterize both pressure and temperature)
are extremely stable over time, these simple offset corrections compensate for the majority of
transducer errors over time. For this reason, a Re-zero may be the only calibration adjustment
required by many applications. For those applications requiring more accuracy, an optional
single-point Span-only calibration adjustment will be described in Section 4.3. An improved
multi-point calibration adjustment, integrating both the Re-zero and Span calibration process will
be described in Section 4.4.
For Model 9116, with integral DH200 pneumatic transducers, internal manifolds and valves
allow a Re-zero calibration to be accomplished easily and automatically.
When instructed to execute a Calculate and Set Offsets (‘h’) command, the NetScanner
™
System module will automatically perform the Re-zero adjustment calibration, and then update
the offset coefficients in its volatile memory. It will subsequently use the newly calculated terms
for all future engineering-unit calculations until power is lost to the module.
Note
When using the Calculate and Set Offsets command (‘h’), only local
terms in the module’s volatile main memory (RAM) are updated.
Under normal operation, it is not recommended to store these new
coefficients in transducer non-volatile memory. Instead, the re-zero
should be performed at regular intervals..
4.2.1. Re-zero Calibration Valve Control
When instructed to execute a Re-zero (Calculate and Set Offsets (‘h’)) command, Model 9116
modules will normally shift the internal calibration valve into the CAL position and use the
pressures present at the CAL and CAL REF inputs for the “minimum” (e.g., zero) calibration
pressure. After the Re-zero adjustment is complete, the Model 9116 calibration valve will be
placed in the RUN position. This automatic shift of the calibration valve can be disabled through
use of the Set Operating Options (‘w’) (option index=0B hex) command. This allows
independent control of the calibration valve by the user using other options (see option indexes
= 0C and 12 hex) of the same command.