2. Before you begin
2.2. Transmitter/Communication characteristics
6 MC Toolkit (MCT404) User Manual Revision 3
The sensor also includes a PROM, (2), which is Non-Volatile Memory (NVM) that stores
"characterization" constants written at the factory, and calibration constants, which can be written at the
factory and/or at the user's site. The data in NVM is used in an algorithm in the microprocessor, (3),
which is executed continuously to calculate the input value.
Figure 2-1 Honeywell ST 3000/ ST 800 Smart Transmitter - Analog mode
The characterization constants, which are written at the factory, are derived from highly precise testing of
the sensor's response over a range of temperatures, and from the Lower Range Limit (LRL) to the Upper
Range Limit (URL) of the sensor. The purpose of the characterization constants is to compensate for
very small inaccuracies in the sensor that are introduced by variations inherent in construction materials,
and to ensure that the calculated input is a high-fidelity representation of the analog input (linear or
square root), with a precise "zero" reference.
Input Calibration ("Corrects")
To optimize accuracy, the PROM includes storage for calibration constants: Correct Input Zero, Correct
LRV, and Correct URV.
The corrects constants provide for optimum accuracy in that they enable fine-tuning of the input
calculations, by first correcting at zero input, then bounding the input calculations at your operating range.
That is, corrections are applied at the Lower Range Value (LRV) and the Upper Range Value (URV).
Factory calibration can be specified in the purchase order. Also, if precision equipment, suitable
environment, and required skill are available at your site, input calibration can be done locally.
Reset Corrects
In some cases, the calibration procedure yields unsatisfactory results such that the Corrects constants
must be removed from memory. The Reset Corrects erases all three corrects constants, so that only the
factory-written characterization constants will be retained in the PROM.
Digital Communication Path
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