38
APPENDIX A — ANALOG FUNCTIONS
The User Configurable Analog Inputs have several
parameters that affect the value interpreted from
the A/D reading. In general, the following equation
determines the final User Configurable Analog Input
result:
Result = Scale (Function (Calibrate (Raw A/D read-
ing)))
For functions that require 4 coefficients for a polyno-
mial, the calibration factor has to be incorporated in
the polynomial coefficients. In this case, the follow-
ing equation determines the final User Configurable
Analog Input result:
Result = Scale (Function (Raw A/D reading))
The RMS Analog Inputs have a calibration parameter
and a scaling parameter that affect the value inter-
preted from the A/D reading. The following equation
determines the final RMS Analog Input result:
Result = Scale (Calibrate (RMS Function (Raw A/D
reading)))
Although the calibration and scaling adjustments
exist for the remaining Analog Inputs (i.e. derived
channels), it is unlikely they will be used. The
remaining Analog Inputs are derived from other ana-
log inputs that have already been adjusted. If further
adjustment is needed, then the following equation
determines the final Analog Input result:
Result = Scale (Calibrate (RMS Function (Raw A/D
reading)))
These derived inputs have more complex interactions
with the hardware, so care should be taken if adjust-
ments are used.
The conversion functions are described below. One of
these functions is a 16 bit floating point polynomial
- GEN_FP_POLY. This function should only be used
as an extreme last resort as it is processor time inten-
sive. The other integer polynomial functions should
be sufficient for converting the A/D input data.
The coefficients for the conversion functions need to
be adjusted for working in the A/D counts realm as
opposed to the voltage realm. Multiply A/D reading
voltage by 1023/5 to convert to A/D reading counts.
Also, the coefficient scaling is in powers of 2 to
expedite processing of math operations using shifts
instead of multiply and divide. The following types
of Analog Input functions are implemented in the
firmware.
THERMISTOR:
PRESSURE:
POLY_3RD:
Third order polynomial with 4 coefficients and a scal-
ing factor
X
=
raw_analog
(AX3 + BX2 + CX + D) * S
Where:
A, B, C, D are polynomial coefficients
S is the scaling factor
Coefficient 3 = A * 10243
Coefficient 2 = B * 10242
Coefficient 1 = C * 1024
Calibration
=
D
Scaling
= S * 1024
POLY_2ND:
Second order polynomial with 3 coefficients, a scal-
ing factor, and a calibration factor
X = M * raw_analog
(AX2 + BX + C) * S
Where:
M is the calibration factor
A, B, C are polynomial coefficients
S is the scaling factor
Calibration = M * 1024
Coefficient 3 = A * 10242
Coefficient 2 = B * 1024
Coefficient 1 = C
Scaling
= S * 1024
LINEAR:
POLY_1ST:
First order polynomial with 2 coefficients, a scaling
factor, and a calibration factor
X = M * raw_analog
(AX + B) * S
Where:
M is the calibration factor
A, B are polynomial coefficients
S is the scaling factor
Calibration = M * 1024
Coefficient 2 = A * 1024
Coefficient 1 = B
Scaling
= S * 1024
POLY_1ST_N1:
First order polynomial with 3 coefficients, a scaling
factor, and a calibration factor
X = M * raw_analog
(A + BX + CX-1) * S
Appendix A
H-100 Control Panel Technical Manual
