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3.2 Correction Algorithms
3.2.1 Pressure
One of 2 similar algorithms for converting IPT temperature and pressure channel ADC values into
corrected pressure readings is identified for each IPT. (Section 3.3.2.7 describes how the applicable
algorithm identity is documented in the IPT EEPROM contents.)
Coefficients (A, a1, a2, etc.) for the identified algorithm are stored in the IPT EEPROM. The algorithm
result (Y) is a corrected pressure reading in pounds per square inch (PSI). ADC values from the
temperature channel (normalized) are used to correct the readings for thermal effects.
3.2.1.1 Algorithm #1
Y = A + (F1 × p) + (F2 × p
Where:
F1 = a1 + (b1 × t) + (c1 × t
F2 = a2 + (b2 × t) + (c2 × t
F3 = a3 + (b3 × t) + (c3 × t
F4 = a4 + (b4 × t) + (c4 × t
F5 = a5 + (b5 × t) + (c5 × t
F6 = a6 + (b6 × t) + (c6 × t
Output: Y = pressure value in PSI
Inputs: p = 24-bit pressure channel ADC value, normalized 0 – 1
Normalized pressure channel ADC value = pressure channel ADC value / 16,777,215
t = 16-bit temperature channel ADC value, normalized 0 - 1
Normalized temperature channel ADC value = temperature channel ADC value / 65,535
3.2.1.1.1 Horner's Method, Algorithm #1
Horner's method is a suggested microcontroller-friendly alternative for evaluating the above equations:
Y = A + p(F1 + p(F2 + p(F3 +p(F4 + p(F5 + p(F6))))))
F1 = a1 + t(b1 + t(c1 + t(d1 + t(e1 + t(fa1)))))
F2 = a2 + t(b2 + t(c2 + t(d2 + t(e2 + t(fa2)))))
F3 = a3 + t(b3 + t(c3 + t(d3 + t(e3 + t(fa3)))))
F4 = a4 + t(b4 + t(c4 + t(d4 + t(e4 + t(fa4)))))
F5 = a5 + t(b5 + t(c5 + t(d5 + t(e5 + t(fa5)))))
F6 = a6 + t(b6 + t(c6 + t(d6 + t(e6 + t(fa6)))))
2
3
) + (F3 × p
) + (F4 × p
2
3
) + (d1 × t
) + (e1 × t
2
3
) + (d2 × t
) + (e2 × t
2
3
) + (d3 × t
) + (e3 × t
2
3
) + (d4 × t
) + (e4 × t
2
3
) + (d5 × t
) + (e5 × t
2
3
) + (d6 × t
) + (e6 × t
4
5
) + (F5 × p
) + (F6 × p
4
5
) + (fa1 × t
)
4
5
) + (fa2 × t
)
4
5
) + (fa3 × t
)
4
5
) + (fa4 × t
)
4
5
) + (fa5 × t
)
4
5
) + (fa6 × t
)
(6 multiplies, 6 additions)
(5 multiplies, 5 additions)
(5 multiplies, 5 additions)
(5 multiplies, 5 additions)
(5 multiplies, 5 additions)
(5 multiplies, 5 additions)
(5 multiplies, 5 additions)
Total:
36 multiplies, 36 additions
6
)
12
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