measure.cpp File Reference

#include "measure.h"

Enumerations
enum	register_mask {   RDY =1<<7, CHAN =3<<5, CON =1<<4, DEPTH =3<<2,   PGA =3<<0 }
	Bitmasks for the MCP3424 status/control register. More...

Functions
int	measure (struct pt *pt, struct measure_stack &m)
	Captures a measurement from the three probes. More...
int	baseline (struct pt *pt, struct measure_stack &m, char &rdv)
	Calculates baseline temperature. More...
int	delta (struct pt *pt, struct measure_stack &m, char &rdv)
	Calculates temperature delta and sapflow. More...
double	rtd_calc (int32_t raw)
	Converts raw measurement into degrees Celcius. More...
int	mcp3424_measure (struct pt *pt, uint8_t addr, uint8_t ch, int32_t &result)
	Measures the value of a single ADC channel. More...

Enumeration Type Documentation

register_mask

enum register_mask

Bitmasks for the MCP3424 status/control register.

Enumerator
RDY	result ready
CHAN	Channel 0-3.
CON	Continuous/One-Shot.
DEPTH	Bit depth 12-18.
PGA	Gain of 1-8.

Function Documentation

baseline()

int baseline	(	struct pt *	pt,
		struct measure_stack &	m,
		char &	rdv
	)

Calculates baseline temperature.

This is a protothread that averages 10 samples of data to determine the "initial" or "baseline" temperature of the tree. It should be used before the heater is turned on.

Parameters

pt	A pointer to the protothread control structure. Don't forget to initialize the control structure in setup().
m	Persistent storage for this thread, like a private stack.
rdv	Rendezvous to ensure all baseline() instances stop at the same point

Returns

the status of the protothread (Waiting, yeilded, exited, or ended)

References cout(), measure_stack::i, measure_stack::latest, temperature::lower, measure_stack::maxtemp, measure_stack::reference, measure_stack::sem, measure_stack::treeID, and temperature::upper.

Referenced by schedule().

delta()

int delta	(	struct pt *	pt,
		struct measure_stack &	m,
		char &	rdv
	)

Calculates temperature delta and sapflow.

This is a protothread that calculates the sap flow by averaging measurements over 40 seconds. It also calls other functions to get the weight, package the data, log to an SD card, and send the information over LoRa.

Parameters

pt	A pointer to the protothread control structure.
m	Persistent storage for this thread, like a private stack.
rdv	Rendezvous to ensure all delta() instances stop at the same point

Returns

the status of the protothread (Waiting, yeilded, exited, or ended)

We compute sapflow using the following formula:: sapflow = k / x * log(v1 / v2) / 3600

• k is an empirical constant
• x is the distance between the probes
• v1 is temperature increase of the upper probe from its baseline temperature
• v2 is the temperature increase of the lower probe from its baseline temperature
• 3600 is the number of seconds in an hour

In order to get a smoother result, we are takng the average of this calculation over a period of 40 seconds. Burges et. al. (2001) suggests that this value should converge.

References cout(), measure_stack::flow, measure_stack::i, int2str(), measure_stack::latest, temperature::lower, measure_stack::reference, rtc_ds, measure_stack::sem, measure_stack::treeID, and temperature::upper.

Referenced by schedule().

mcp3424_measure()

int mcp3424_measure	(	struct pt *	pt,
		uint8_t	addr,
		uint8_t	channel,
		int32_t &	result
	)

Measures the value of a single ADC channel.

Parameters

pt	A pointer to the protothread control structure
addr	The 7-bit I2C address of the ADC. If you choose, you can enter only the last three bits (0-7).
channel	The measurement channel. Valid inputs are 1-4.
result	The raw 18-bit signed ADC value. Result is bit-extended to 32 bits.

Returns

the status of the protothread (Waiting, yeilded, exited, or ended)

References CHAN, DEPTH, PGA, and RDY.

Referenced by measure().

measure()

int measure	(	struct pt *	pt,
		struct measure_stack &	m
	)

Captures a measurement from the three probes.

This is a protothread that reads the temperature from three RTD amplifiers connected to the probes in the tree. It stores the result in the struct paramter "latest" and logs to the SD card.

Parameters

pt	A pointer to the protothread control structure. The default parameter is correct. Don't forget to initialize the control structure in setup().
m	Persistent storage for this thread, like a private stack.

Returns

the status of the protothread (Waiting, yeilded, exited, or ended)

References measure_stack::addr, measure_stack::child, cout(), temperature::heater, int2str(), measure_stack::latest, temperature::lower, measure_stack::maxtemp, mcp3424_measure(), measure_stack::raw, rtc_ds, rtd_calc(), measure_stack::sem, measure_stack::treeID, and temperature::upper.

Referenced by loop().

rtd_calc()

double rtd_calc

(

int32_t

raw

)

Converts raw measurement into degrees Celcius.

Parameters

raw	The value measured by the ADC

Returns

temperature in Celcius

Referenced by measure().