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heater.c: Add comments about units of PID variables and constants.

This commit is contained in:
David Forrest 2014-03-17 16:01:45 -04:00 committed by Markus Hitter
parent e771d2340e
commit 034d8445fd
1 changed files with 12 additions and 12 deletions
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24
heater.c
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@ -49,15 +49,15 @@ static const heater_definition_t heaters[NUM_HEATERS] =
See http://www.eetimes.com/design/embedded/4211211/PID-without-a-PhD for the full story
*/
struct {
int32_t p_factor; ///< scaled P factor
int32_t i_factor; ///< scaled I factor
int32_t d_factor; ///< scaled D factor
int32_t p_factor; ///< scaled P factor: mibicounts/qc
int32_t i_factor; ///< scaled I factor: mibicounts/(qC*qs)
int32_t d_factor; ///< scaled D factor: mibicounts/(qc/(TH_COUNT*qs))
int16_t i_limit; ///< scaled I limit, such that \f$-i_{limit} < i_{factor} < i_{limit}\f$
} heaters_pid[NUM_HEATERS];
/// \brief this struct holds the runtime heater data- PID integrator history, temperature history, sanity checker
struct {
int16_t heater_i; ///< integrator, \f$-i_{limit} < \sum{\Delta t} < i_{limit}\f$
int16_t heater_i; ///< integrator, \f$-i_{limit} < \sum{4*eC*\Delta t} < i_{limit}\f$
uint16_t temp_history[TH_COUNT]; ///< store last TH_COUNT readings in a ring, so we can smooth out our differentiator
uint8_t temp_history_pointer; ///< pointer to last entry in ring
@ -76,13 +76,13 @@ struct {
#define HEATER_THRESHOLD 8
#endif
/// default scaled P factor, equivalent to 8.0
/// default scaled P factor, equivalent to 8.0 counts/qC or 32 counts/C
#define DEFAULT_P 8192
/// default scaled I factor, equivalent to 0.5
/// default scaled I factor, equivalent to 0.5 counts/(qC*qs) or 8 counts/C*s
#define DEFAULT_I 512
/// default scaled D factor, equivalent to 24
/// default scaled D factor, equivalent to 24 counts/(qc/(TH_COUNT*qs)) or 192 counts/(C/s)
#define DEFAULT_D 24576
/// default scaled I limit
/// default scaled I limit, equivalent to 384 qC*qs, or 24 C*s
#define DEFAULT_I_LIMIT 384
#ifdef EECONFIG
@ -305,22 +305,22 @@ void heater_tick(heater_t h, temp_type_t type, uint16_t current_temp, uint16_t t
// PID stuff
// proportional
heater_p = t_error;
heater_p = t_error; // Units: qC where 4qC=1C
// integral
heaters_runtime[h].heater_i += t_error;
heaters_runtime[h].heater_i += t_error; // Units: qC*qs where 16qC*qs=1C*s
// prevent integrator wind-up
if (heaters_runtime[h].heater_i > heaters_pid[h].i_limit)
heaters_runtime[h].heater_i = heaters_pid[h].i_limit;
else if (heaters_runtime[h].heater_i < -heaters_pid[h].i_limit)
heaters_runtime[h].heater_i = -heaters_pid[h].i_limit;
// derivative
// derivative. Units: qC/(TH_COUNT*qs) where 1C/s=TH_COUNT*4qC/4qs=8qC/qs)
// note: D follows temp rather than error so there's no large derivative when the target changes
heater_d = heaters_runtime[h].temp_history[heaters_runtime[h].temp_history_pointer] - current_temp;
// combine factors
int32_t pid_output_intermed = (
int32_t pid_output_intermed = ( // Units: counts
(
(((int32_t) heater_p) * heaters_pid[h].p_factor) +
(((int32_t) heaters_runtime[h].heater_i) * heaters_pid[h].i_factor) +