T7Convert.hpp

Go to the documentation of this file.

#pragma once
 
// T7 volts -> engineering units: psi for a PT, kg for a load cell, C for a type K thermocouple.
// The same units, and the same Elodin field names, as the ESP32 boards' calibrated tables, so the
// GUI can treat a T7 channel as one more PT / LC / TC.
//
// Every function returns NaN when it cannot produce a number (a missing parameter, a reading off
// the end of a thermocouple curve); the caller publishes nothing rather than a plausible zero.
 
#include "config/T7Config.hpp"
 
namespace fsw {
namespace t7 {
 
/**
 * The T7's internal temperature sensor (an LM94021 on AIN14) reads "Device temperature K =
 * volts * -92.6 + 467.6" (T-series datasheet 18.0 Internal Temp Sensor; the same values are the
 * nominal Temp_Slope / Temp_Offset in 20.0.1 T7 Calibration Constants). Each unit's own slope and
 * offset are in flash. The offset is taken per unit at stream start instead of from the nominal
 * 467.6 K: t7_bridge reads the device's own calibrated TEMPERATURE_DEVICE_K beside AIN14 (before
 * the stream, which blocks command-response reads of the sensor) and solves for it, so the nominal
 * slope only has to hold over the few kelvin the box drifts. (-92.379 / 465.129, used here before,
 * are the U6's nominal constants, not the T7's.)
 */
constexpr double kAin14SlopeKPerV = -92.6;
/** Nominal AIN14 offset (K), datasheet 18.0. Only the fake T7 uses it; a real one is solved. */
constexpr double kAin14NominalOffsetK = 467.6;
 
/** AIN14 offset (K) that makes slope*ain14_v land on the device's own temperature reading. */
double cjc_device_offset_k(double device_temp_k, double ain14_v);
 
/** Cold-junction temperature (C) from a streamed AIN14 reading. */
double cjc_temp_c(double ain14_v, double device_offset_k, double cjc_offset_k);
 
/** PT: linear between the signal's zero and full-scale outputs. */
double pt_psi(double volts, const config::T7Channel& ch);
 
/** LC: a bridge's output is sensitivity x excitation at rated load. */
double lc_kg(double volts, const config::T7Channel& ch);
 
/** Type K thermocouple: the measured EMF plus the EMF the cold junction subtracts. */
double tc_c(double volts, double cold_junction_c);
 
/** RTD on an LJTick-Resistance: the divider's output volts -> the RTD's ohms. NaN outside
 *  (0, vref_v), where the divider cannot be inverted (open or shorted RTD). */
double rtd_ohms(double volts, const config::T7Channel& ch);
 
/** RTD: ohms -> C on the IEC 60751 curve (full Callendar-Van Dusen, C term below 0 C). */
double rtd_c(double volts, const config::T7Channel& ch);
 
/** The Elodin field a calibrated channel of this kind publishes ("pressure_psi", ...), or ""
 *  for a kind with no calibrated table (VOLTAGE). Same names as the ESP32 boards' tables. */
const char* calibrated_field(const std::string& kind);
 
}  // namespace t7
}  // namespace fsw