Spa control system

A spa control system which calculates the time required to heat the water in the spa system to a desired temperature. From that information, the heating rate of the spa system can be determined, and the heating element of the spa system can be activated at the proper time to raise the temperature of the water to a selected temperature by a desired time. The spa system also monitors information which might show errors in the operation of the spa system such as a blockage in the flow of water over the heating element in the spa system.

FIELD OF THE INVENTION 
This invention relates to the development of a spa control system. More 
particularly, this invention relates to a spa control system which uses an 
interconnection panel and a control panel to effectively control various 
operating functions of the spa. 
BACKGROUND OF THE INVENTION 
The design of systems to control spas is complicated by the environment of 
the spa. Typically, spa control systems contain heating elements, 
controls, switches, and wiring harnesses which deteriorate when exposed to 
moisture or extreme levels of humidity and a hostile chemical environment. 
Since the chemically treated, heated water of the spa raises the humidity 
level and produces corrosive gases, the atmosphere surrounding the 
controls of the spa unit is inherently corrosive to spa control systems. 
The accuracy of the temperature of the spa water is essential to the safety 
and comfort of the spa user. This temperature is difficult to accurately 
control, since the temperature of the water can vary rapidly depending on 
the number of spa users, the ambient temperature of the air, and other 
environmental factors. To conserve energy, the spa temperature is 
customarily raised to the desired level shortly before the expected use of 
the spa, and is not maintained at a constant temperature when the spa is 
unattended. Depending on the use of the spa, the temperature of the spa 
water may be cycled several times per day. During these cycles, the 
control of the water temperature is difficult to maintain without 
overheating or underheating the water. Typically, a spa control system 
merely heats the water with a heating element until the temperature of the 
water matches a predetermined setting selected by the spa user. Since the 
heating element is not turned off until that desired water temperature is 
reached, the residual heat in the heating element may increase the 
temperature of the water beyond the actual temperature desired. 
Conversely, the location of the temperature sensor may be located in the 
spa in such a fashion that it does not sense the actual, median water 
temperature. Accordingly, the heating element may be turned off before the 
temperature of the water reaches the desired level. 
Present spa controllers operate on line voltages which can present a safety 
hazard to the spa users. To meet desired safety specifications, these 
controls are typically located away from the spa, however, this separation 
is inconvenient to the spa user. 
SUMMARY OF THE INVENTION 
The present invention overcomes the foregoing difficulties by providing a 
spa control system which accurately and efficiently controls the operation 
of the spa and is not adversely affected by the corrosive environment 
surrounding the spa. The spa temperature control system generally 
comprises a heating element, a sensor for detecting the temperature of the 
water, and a microcomputer for processing signals generated by said sensor 
and for activating and deactivating the heating element. In one embodiment 
of the invention, the microcomputer assesses the time necessary to heat 
water from an initial temperature to a selected temperature. From this 
information, the heating rate of the water can be calculated. The heating 
rate can be stored by the microcomputer and can be used to determine the 
start time necessary to heat the spa water from an initial temperature to 
a selected temperature by a desired time. In the same or another 
embodiment of the invention, the temperature difference between two 
sensors in the spa system can be monitored to detect problems in the 
system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 illustrate a block diagram of the overall spa control system. 
The spa control system uses an intelligent microcomputer 10 to monitor and 
control the operation of the spa (not shown). The system uses solid state 
electronic components which eliminate many of the problems associated with 
traditional mechanical timer and relay control systems. The use of solid 
state electronic components increases the reliability of the system and 
reduces the maintenance necessary to maintain the spa in operable 
condition. 
Referring to FIG. 1, the external system generally comprises a spa control 
panel 12 which is connected to a system innerconnection panel 14. The 
system innerconnection panel 14 is also connected to power input 16, to 
various sensors which detect parameters at such a flow rate 18, 
temperature 20, and pH of the water 22, and also the mechanical and 
electrical components of the spa, such as the pump 24, heater 26, blower 
28, and lights 30. The heater 26 may be interlocked to the pump 24 so that 
the pump 24 is continuously pumping water over the heating element (not 
shown) of the heater 26 while the heater 26 is activated. This prevents a 
"hot spot" from developing in the spa system which could damage the 
components of the spa or give erroneous measurements. 
The system is a microcomputer-based system. In addition to, or as part of, 
the microcomputer 10, the system utilizes several other devices as 
generally shown in FIGS. 1 and 2. While the control program runs on the 
microcomputer 10, it is directly responsible for the management of the 
system hardware. The following description briefly summarizes the major 
devices: 
NOVRAM 32 This is a nonvolatile RAM device that is used to store the system 
calibration values as well as providing RAM expansion for the 
microcomputer 10. An EEROM image of the current image is stored when the 
powerfail interrupt is posted to the microcomputer 10 and restored when 
the microcomputer 10 powers up. 
RTC 34 This is a realtime clock device that provides a clock value. It is 
the timebase for events that are scheduled by time of day as well as a 
timer for events that are measured in seconds. 
A/D 36 This is an analog to digital converter that converts voltage inputs 
after signal conditioning 37 to digital numeric representations. It 
provides three values: spa temperature, heater temperature (both labelled 
20) and pH value 22. 
DISPLAY DRIVER or INTERFACE 38 This device accepts a bitstream 39 from the 
microcomputer and drives the display 40 for the spa control panel 12. A 
bit is input for each segment on the display. 
FIG. 2 illustrates a block diagram of the spa control system and its 
associated components. The electronics in the spa control system are 
designed to handle temperature extremes of minus twenty to plus seventy 
degrees Centigrade. The technology used in this design of interface 
components is Complementary Metal Oxide Semiconductors (CMOS) which is low 
in power consumption and high in reliability. The microcomputer 10 is 
typically an 8-bit control device with an 8-bit data bus 42. Its function 
is to execute instructions, control processes, make logical decisions and 
compute values. The microcomputer 10 operates at a clock speed of 
typically two megahertz and can make thousands of calculations per second. 
The microcomputer 10 reads instructions from the memory, such as EPROM 44 
and then executes the appropriate actions. 
The Eraseable Programmable Read Only Memory (EPROM) 44 stores the 
instructions for the microcomputer 10 to execute. Once a program is 
created the final software is loaded into the EPROM 44. The EPROM 44 can 
be modified to add new features, or additional EPROMs (not shown) can be 
connected to manage different functions and applications. The Random 
Access Memory (RAM) 32 is a memory device which stores temporary 
information while the information is being processed by the microcomputer 
10. The RAM 32 only reads and writes data, and can hold data for future 
reference even after the main power 16 is turned off. The RAM 32 stores 
data such as the number of hours on the heater 26, the number of times 
that the temperature of the spa exceeds the pre-selected temperature, and 
other information. 
The Real Time Clock (RTC) 34 shows the proper time of day which is 
calculated after the time and date are initially set. The microcomputer 
uses this information to schedule events concerning the operation of the 
spa, such as when the spa is turned on, when the water is circulated, and 
other events. The RTC 34 is backed with a battery or similar device (not 
shown) so that it maintains the accurate time when the main power supply 
is turned off. 
The display interface 38 is responsible for driving and updating the 
display device 40. When the microcomputer 10 sends information to this 
block it is decoded and displayed on the screen 46. 
The display screen 46 is typically a vacuum-fluorescent type which has a 
blue-green color. The display contains four seven-segment characters, and 
colon. The Display Interface 38 represents circuitry which drives and 
updates the display device. Information from the microcomputer 10 is 
decoded and displayed on the screen 46 by the means of the interface 38. 
The data remains on the screen 46 until the microcomputer 10 sends a new 
message or the system is reset or powered off. 
The keyboard 48 (FIGS. 1 and 6) shown is a flat panel membrane style which 
is incorporated into the front panel. One type of keyboard 48 has ten 
push-buttons 50 and nine translucent cut-outs for backlighting of Light 
Emitting Diodes (LEDS) 52. The keyboard 50 is mounted on bezel 54 to 
provide a firm surface when depressing the buttons 50. The keyboard 
interface 56 provides circuitry which transmits information from the 
keyboard 48 to the microcomputer 10. The keyboard interface 56 acts as an 
array of on/off switches that correspond to each keypad. The microcomputer 
10 scans these switches as on/off, switch type input bits. 
The Digital Outputs 58 drive the external spa devices, such as the blower 
24, heater 26, pump 28 and other auxiliary devices. The low voltage 
signals are optically isolated 60 and then drive a TRIAC device 62 which 
provides the high voltage and high current required by the external 
devices. 
As previously set forth, the system innerconnection panel 14 connects the 
components of the spa control system. Referring to FIG. 3, the power 16 to 
the system innerconnection panel 14 is supplied through usual power 
supply. The Ground Fault Current Interrupter (GFCI) 64 provides protection 
to the system innerconnection panel 14 if an imbalance of current flow 
occurs through the Door Interlock between the Input and the Output of the 
GFCI. The GFCI 64 prevents voltage and current from entering the system 
after the device has been triggered. After the power has passed through 
the GFCI 64, the Power Supply 66 converts the 110 or 220 Volt AC into the 
low voltage and low power required by some components of the system. The 
power supply 66 also contains the backup battery or other device (not 
separately shown) used to provide power to the RTC 34 when the main power 
is turned off. 
The Opto-Isolators 60 receive signals from the spa control panel 12 which 
designate the operation of the proper output device. The Opto-Isolators 60 
isolate the low voltage and current control system from the high voltage 
and high current of the main power supply 16. These devices in conjunction 
with Triacs 62 also provide synchronization with the zero volts crossing 
of the AC power 16 to switch devices on/off when power is minimal to avoid 
stressing devices. Connected to the Opto-Isolators 60 are the Triacs 62, 
which are solid state devices used to drive high voltage and high current 
output devices with alternating current. Triacs 62 function as relays, 
except that Triacs 62 are electronic devices that do not contain any 
moving parts. Typically, the Triac 62 to a heating element may be rated at 
forty amps maximum current, and the Triacs 62 to other output devices 
might typically be rated at twenty-five amps. Connected to the Triacs 62 
is a field connection board 70 which mechanically permits the connection 
and disconnection of field devices such as a pump motor 24, blower motor 
28, heater core 26, or a spa light 72. 
The output devices are connected to the field connection board 70 by 
connectors 71. 
Referring again to FIG. 2 Analog Input section 36 converts information from 
various sensors 20, 22 into digital information so that the data can be 
read by the microcomputer 10. The converter 36 translates the analog 
information into digital information through, for example, dual slope 
integration which permits fast and accurate conversion. The accuracy of 
the A-D section 36 typically is 8 bits or a resolution of 1 out of 256. 
The signals from external probes and sensors 20, 22 are conditioned by 
amplifying, filtering, or conditioning the signals 37 so that the A-D 
converter 36 can make an accurate conversion. The Signal Conditioning 
section 37 also receives the small signals from external probes 20, 22 and 
amplifies it to a level where the A-D converter 36 can make an accurate 
conversion. This section 37 also provides transient and surge protection 
to reduce normal and common mode rejection noise. 
FIG. 4 illustrates a functional block diagram of the software which 
operates the microcomputer 10. The final software code is encrypted on the 
EPROM 44 (FIG. 2) for operating the microcomputer 10. The main program 80 
schedules the operation of all other subprograms and performs general 
housekeeping chores, such as memory management, timer control, interrupt 
handling and the scheduling of tasks. 
The keyboard monitor routine 82 scans the keyboard and is triggered by the 
operation of any key. The key signal from the digital input is then 
decoded, and the main program 80 is triggered to initiate a series of 
programmed events. The program ignores multiple key depressions and 
erroneous entries and operates only upon the signal generated from a 
proper key entry. The display control program 84 converts data from the 
EPROM 44 to readable messages which can be shown on the display 46. The 
display control 84 handles the timing of the signals so that the display 
46 performs in an efficient and proper manner. The alarm control 86 
monitors the proper operation of the entire spa system. If the system 
malfunctions or otherwise operates incorrectly as measured by the input 
signals or data inferred from the input signals, the alarm will signal the 
malfunction to the panel 12. Examples of malfunctions in the system that 
might occur are the malfunction of the heater 26 and whether the pH 22 
levels are within an acceptable range. In the event of a malfunction, a 
signal will be sent to the display controller 84 to display the alert 
signal and to alert the spa user of the malfunction. 
The Analog Conversion Program 88 manipulates the converter circuitry 36 to 
read and convert analog input signals from sensors to digital information. 
This program also converts the digital information to engineering units 
for the purposes of display and comparison. 
The RTC control program 90 controls all interaction with the Real Time 
Clock 34. The program is responsible for loading data for future events. 
The PID Control 92 defines a proportional, integral and derivative control 
program. This program 92 performs the closed loop control of temperature 
using the temperature input 20 as its variable to be controlled and the 
heating elements 26 and the output to maintain control. The program 92 
monitors the temperature 20 of the water and determines when the heater 26 
should be engaged. The program issues a command which activates the heater 
26, and then monitors the temperature 20 to determine when the heater 26 
should be turned off. The program is unique in that it also monitors the 
rate of decrease and the rate of increase of the water temperature so that 
the final temperature of the water is not higher or lower than the 
selected temperature beyond the control supplied by *derivative control. 
The spa control system can achieve an accuracy of plus or minus one degree 
Fahrenheit with the heating and monitoring elements. 
The output control program 94 issues commands to the output components to 
turn on the Triacs 62 for control of the pump 24, heater 26, blower 28, 
lights 30 and other components. The input scanning program 96 monitors 
devices such as push buttons and switches. The pH algorithm 98 converts 
raw digital data received from the A-D converter 36 on the pH input 22 and 
converts this data to standard pH units of measure. 
FIG. 4 provides an overview of the program organization. Three events are 
handled by the system. Reset occurs when the system is powered up. It 
performs system initialization, enables the other events, and then calls 
the main program. The timer interrupt occurs periodically and inputs that 
require periodic polling are scanned. The power fail interrupt occurs when 
system power is failing. The primary purpose of this handler is to save 
the current system operating parameters within the time remaining before 
power fails completely. The function of certain subroutines in one 
embodiment of the system are described in detail below. 
The system initialization routine is invoked by powerup reset. This routine 
is responsible for initialization of all devices and data structures. The 
tasks it performs are: 
Clear all RAM 
Turn off all control outputs 
Digital I/O initialization 
Restore NOVRAM image (to restore previous system configuration) 
Clear display 
Initialize the RTC. It the time was lost, it is reset to 12:00 midnight 
Initialize keyboard scanner 
Test the NOVRAM image for validity. If the image is invalid, create 
fallback image and post warning 
Test EPROM (program space) memory 
Display 110/220 volt setting 
Perform RTC update test (takes a couple seconds) 
Enable timer and powerfail interrupts 
Jump to main program 
The timer interrupt handler responds to the periodic timer interrupts. It 
scans I/O devices that require constant scanning for system operation and 
provides a higher frequency timer base than the one second resolution 
provided by the real time clock. The operations this handler executes are: 
Save interrupted program's context 
Update high speed clock value for synchronization with main program 
Scan keyboard 
Poll real time clock and if seconds have changed, provide one second timer 
update 
Read in one analog channel. Provide raw input correction and calculate 
engineering units (temperature values are curve-fitted, and pH values are 
temperature corrected) 
Restore interrupted program's context 
Return to the interrupted program 
The powerfail interrupt is furnished by a level-monitoring circuit which 
monitors power loss on system input power. When a decline is detected, an 
interrupt is posted to the microcomputer. The powerfail handler is invoked 
when this interrupt is posted. It is responsible for saving the current 
system configuration and for shutting the system down in an orderly 
fashion. The tasks it performs are: 
Mask all interrupts 
Save system configuration (this includes operating parameters as well as 
user settings) 
Turn off all spa controls 
Display "Fail" 
Monitor powerfail interrupt for power restoration (brown out). If powerfail 
is cleared and remains cleared for approximately one second, the powerup 
reset handler is called. 
The main program performs the bulk of the operations performed by the 
system controller. It synchronizes with the timer interrupt so that a 
reasonably constant time base is used. A state machine is maintained to 
determine how keyboard inputs are to be interpreted and what is to be 
displayed. The following tasks are performed by the main program: 
On initial (powerup) entry, pause to allow timer interrupt handler time to 
build valid input values 
Synchronize with timer interrupt. While waiting for timer, drive buzzer 
output. 
Update the general timer used by state handlers for timeouts 
Run flasher manager 
Get current keyboard inputs 
If any keyboard inputs are available, post buzzer output request and reset 
the "system unattended" timer 
Handle keyboard inputs for maintenance mode entry/exit 
Call control manager keyboard input handler 
Call current state manager's keyboard handler routine 
Handle remaining function keyboard inputs to drive state changes 
Go to current state's display handler 
Call control manager to drive system controls 
Go back to the timer synchronization step (step 2) 
Operator settings can be controlled by keys on the system keypad which are 
used to select modes that allow the operator to change settings that 
control system operations. These are grouped at the right side of the 
keypad. They are: 
Spa temperature 
Spa ready 
Filter maintenance 
Time of day 
Scheduled heating 
All of these functions adhere to a consistent operator interface scheme. 
When the function key is pressed, the LED next to the key is lit. The LED 
remains lit until all steps have been completed or another function has 
been selected. While setting a value, the value is displayed on the screen 
and is flashed. The arrow keys are used to change the displayed value and 
the function key is pressed to proceed to the next step in the setting. 
While changes are being made, the display stops flashing to avoid changes 
occurring while the display is in the off state. Once changes have 
stopped, the display resumes flashing. Changes are honored as they are 
made and the operator can change one step of a function without affecting 
the remaining steps. The current setting can be reviewed by pressing the 
appropriate function key repeatably. When a function that has been defined 
by the operator is currently being executed, the LED next to the 
corresponding button blinks. 
The spa temperature key is used to define the temperature setpoint. This 
function has only one step that allows the setpoint to be changed. 
Pressing the set temperature key again exits the mode. 
The spa ready key is used to define when the spa is to be at a particular 
temperature. The following example would cause the system to bring the spa 
temperature to 102 degrees at 6:30 p.m. 
______________________________________ 
Example 
______________________________________ 
Set the hour of the ready time 
06:P 
Set the minute of the ready time 
06:30 
Set the temperature to be achieved 
102 
Enable/disable this function 
On 
______________________________________ 
The filter maintenance key is used to define an interval during which the 
low speed pump is to be run to filter the spa water. It has the following 
steps: 
Set the hour of the start time 
Set the minute of the start time 
Set the duration of the interval. This value changes in increments of ten 
minutes and can be set from zero to eight hours. 
The time of day is set in two steps. First the hour is set, then the 
minute. Hours are displayed with an "A" or "P" for am and pm indication. 
This scheduled heating function allows the user to define the hysteresis 
that is to be used when the spa is unattended. It also allows a "start 
time" to be defined. The spa will begin heating whenever the temperature 
drops below the low temperature setting or the time matches the start 
time. With an appropriate temperature envelope, this will allow the spa to 
heat once a day while unattended. The following steps are used to define 
this function: 
Set the hour of the start time 
Set the minute of the start time 
Set the high limit of the temperature envelope 
Set the low limit of the temperature envelope 
Enable/disable this function 
The idle mode is used when none of the operator setting functions are 
active. At this time, the display scrolls through a sequence of displays 
that display the systems current state. The time, temperature, pH and 
error indications may be cycled continuously. 
Concerning operator controls, some of the systems control outputs are 
directly controlled by the operator through alternate action inputs on the 
keypad. These are the light, jet and turbo keys. The control, manager's 
keyboard handler accepts these keyboard inputs and changes the current 
output values. These changes are then reflected on the LEDs next to the 
keys. The LEDs are lit when the corresponding control is on. 
Maintenance mode is a special state that is reached by turning the 
maintenance switch to its "on" position. When the maintenance mode is 
active, all controls are turned off and the functions of the keys are 
redefined. When none of the keys are active, "test" is displayed. When 
each key is pressed, its corresponding LED is lit and a value is 
displayed. The arrow keys alternately light all LEDs and display segments 
and then turn all LEDs and segments off. The following is a map of the 
keys and the values displayed in maintenance mode: 
______________________________________ 
SCHEDULED HEAT pH input 
SPA READY spa temperature input 
FILTER heater temperature input 
TIME overtemp time accumulator 
TEMPERATURE heater run accumulator 
JET pump run accumulator 
TURBO turbo run accumulator 
______________________________________ 
Accumulated time values are displayed in thousands of hours. A decimal 
point is placed to autorange the displayed value. 
System calibrations are accessed by pressing the light key while in 
maintenance mode. When the light key is pressed, a series of options are 
displayed. To select a step, or continue it, an arrow key is pressed. To 
get the next selection or return to the "test" display, the light key is 
pressed. The options available are: 
______________________________________ 
CAL0 Calibrate analog channel 0 (spa temperature). 
This is a two point (32 and 104 degree) 
calibration for offset and gain correction. 
CAL1 Calibrate analog channel 1 (heater temperature). 
This is identical to CAL0. 
CAL2 Calibrate analog channel 2 (pH input). This is a 
one point (0 volts) calibration for offset 
correction. 
CPU Display cpu RAM contents. 
nov Display NOVRAM contents. 
rvx.y The software revision is "x.y" 
______________________________________ 
The following describes the modules that make up the system controller and 
further describes the algorithms they contain: 
The module anlgin-routine anlgin routine controls the input of a specified 
analog input channel. The operations it performs are: 
output channel number 
read input value 
The module BCDNEG routine is called to negate a BCD value. 
The module BINBCD routine is called to convert a binary value to a BCD 
value. 
The buzzkey routine is called to determine if the key closure should result 
in the buzzer beeping. "Positive" key values result in the buzzer flag 
being set for "buzzer". 
The buzzer routine is called to drive the buzzer if a key was pressed. The 
buzzer interval is decremented until it is zero and the buzzer stops. 
The buzzoff routine is called to cancel the keyboard buzzer output in 
special cases when the state handler wishes to block certain keys from 
being acknowledged. 
The KBCALO routine is called to handle keyboard inputs while displaying 
"CALO". It allows the user to move on to CAL1 or to select to calibrate 
analog channel 0. 
The KBCAL1 routine is called to handle keyboard inputs while displaying 
"CAL1". It allows the user to move on to CAL2 or to select to calibrate 
analog channel 1. 
The DSPCALO, DSPCAL1, DSPCPH routines display the "CALn" message. 
The KBCLOW routine handles keyboard inputs while scanning the low (32 
degree) value during calibration or channels 0 and 1. The user can select 
to abort or continue. If the choice is to continue and the raw input value 
is in the range 1 . . . 31, then the value is accepted and calibration 
continues to the high step. Otherwise, the low error state is entered. 
The DSPCLOW routine is called to display the raw value while waiting for 
the low (32 degree) input value. It builds a display of the form "Ln:xx" 
where n is 0 or 1 and xx is the raw input value. 
The KBCLERR routine is called when the calibration is in the low error 
state. It allows the user to choose to abort or retry the input of the 
calibration value. 
The DSPCLERR routine is called to display the low calibration error message 
of the form "Lx:Er" where x is 0 or 1. 
The KBCHI routine is called to handle keyboard inputs while the temperature 
calibration is in the high (104 degree) input state. It allows the user to 
abort or accept the current setting. If the current setting is in the 
range 163 . . . 195, the value is accepted. In conjunction with the 
previously obtained low value, a pair of values, m and b, are calculated 
such that with raw value r, m*r+b will result in a corrected value at the 
two calibration points. These two values are stored in NOVRAM and used 
from this point onward in temperature calculations for this channel. The 
system then proceeds to the "done" state. If the input value is not in the 
correct range, the system proceeds to the high error state. 
The DSPCHI routine is called to display the raw input while in the high 
(104 degree) calibration step. It builds a message of the form "Hn:xx: 
where n is 0 or 1 and xx is the raw value. 
The KBCHERR routine is called when the calibration is in the high error 
state. It handles the keyboard input and allows the user to abort the 
sequence or return to the high value input state. 
The DSPCHERR routine is called to display the message "Hn:Er" when the high 
calibration step is in error. "n" is either 0 or 1. 
The KBCDONE routine is called to handle keyboard inputs when the 
calibration is complete. It allows the user to return to the idle 
maintenance mode state. It acts to hold the "done" message until the user 
acknowledges it. 
The DSPCDONE routine is called when the calibration has reached a 
successful conclusion. It displays the message "done". 
GETRAW is a routine local to the calibration module to fetch the 
appropriate raw input from the raw input table. 
The KBCPH routine is called when "CAL2" is displayed. It allows the user to 
choose to move to the next item in the "light" menu or to calibrate the pH 
input. 
The KBCPHI routine is called to handle keyboard inputs when calibrating the 
pH input. It allows the user to abort the operation, or to accept the 
current input. If the current input has an error of less than 32, the 
offset is stored and the calibration goes to the "done" state. If the 
error is too large, the system goes into the pH error state. 
The DSPCPI routine is called to display the current raw pH input during pH 
calibration. It forms a message of the form "PH:xx" where xx is the 
current raw input. 
The KBCPHE routine is called to handle keyboard inputs when the pH 
calibration value has too large an error. It allows the user to abort the 
operation or to retry the calibration. 
The DSPCPE routine is called to display the error message "PH:Er: when the 
calibration value has too large of an error. 
The module control-routine CTLPOLL routine is called by the main program to 
perform the actual output controls. The following tasks are performed: 
Set Ready--if the set ready function is enabled, this section decides if 
the set ready function is to perform any actions. If the current time 
matches the ready time, the set ready temperature is copied to the spa 
temperature setpoint, the spa is marked "attended" and the set ready 
function is disabled to prevent further actions. 
For the Set Ready, as well as for Normal Temperature Control discussed 
infra, the time required to get from the current temperature to the 
desired temperature is calculated and with a fifteen minute hysteresis, 
the decision is made whether to turn the function on, or to turn it off. 
If the function is to be on, a request is posted to the heater to run. 
System Attended--system attendance is checked and if the system is 
unattended, the high speed jet and the turbo controls are turned off. The 
system is marked attended if a key has been pressed within the last 30 
minutes. 
Scheduled Heating--if the scheduled heating function is enabled, this 
section decides if this feature should perform any actions. If the system 
is attended, control is passed to the next section, normal setpoint 
control. If the function is off, the temperature is compared to the low 
setting and the time is compared to the time setting. If appropriate, the 
function is requested, but control is still passed to the "on" section to 
allow it to override the time startup. If the function is on, the 
temperature is compared to the high setting and turned off if the setting 
has been reached. The next section, normal setpoint control, is then 
skipped. 
Normal Temperature Control--this function is executed if the system is 
attended or if the scheduled heating function is not enabled. It compares 
the current temperature to the temperature setpoint to see if the heater 
should be given a request to be on or off from this function. 
Heater/Pump Interlocks--this section handles pump/heater interlocks. It 
requires that the pump runs fifteen seconds before the heater actually 
runs. It also guarantees that the pump runs sixty seconds after the heater 
is turned off. It also interposes at the delay lockout to prevent on/off 
cycling due to fluctuations in control requests. 
110 V Interlocks--units operating on 110 v have limitations on how much 
power can be used at any given moment. The system charges 110/220 
algorithm automatically at power-up. This section also checks the current 
110 v/220 flag and posts a heater shutdown request if this is a 110 v unit 
and either the jet or turbo are on. 
Pump Speed Interlock--this section handles the timing of transfers between 
high and low speed pump operation. A delay of three timer interrupts is 
interposed between the two speeds to prevent the possibility of on/off 
switching on cycle boundaries causing both outputs being on 
simultaneously. 
Low Speed on Requests--the low speed pump requests for heater and heater 
cooling, as well as the filter interval are handled in this section. If a 
heater request is on, then a low speed pump request is posted. If the 
heater cooldown interval is active, a pump request is posted. If the 
current time is within the filter interval, a pump on request is posted. 
Control then passes to the control error handler (CTLERR). 
The Module CTLACT--Routine CTLACT routine performs the following tasks: 
Maintenance/Error Handling--if the system is in maintenance mode, the 
light, turbo and jet outputs are shut off. If the system has detected a 
serious system error (error 1 . . . 8), the turbo and jet outputs are shut 
off. In either case, the heater is shut down. 
Pump Actuation--if any pump requests are posted and no shutdowns are 
requested, the pump is turned on. 
Heater Actuation--if any heater requests are posted and no shutdowns are 
requested, the heater is turned on. Control then passes to the control LED 
handler. 
The Module CTLERR-Routine CTLERR--routine posts two errors and two 
warnings. The errors it checks for are frozen water and mismatch in 
temperature readings (flow error). The warnings it checks for are the 
water being too hot for safe usage and the pH reading out of safe limits. 
The Module CTLKEY-Routine CTLKEY--routine handles directly output-keyboard 
inputs. In particular, it controls the light, jet and turbo. If the system 
is maintenance mode, no keys are processed. If the system is in an error 
state only the light key is processed. The controls are complemented each 
time the corresponding key is pressed. 
The Module CTLLEDS-Routine CTLLEDS--if the module CTLLEDS-routine CTLLEDS 
operates when the system is in maintenance mode, and the LED drive is 
disabled, the light, turbo and jet LEDS are driven solely on the output 
states. The heater LED is driven steadily if the heater is on and flashed 
if the heater is off and has a request posted. The filter, set ready, 
scheduled heat and temperature LEDS are flashed if the corresponding 
function is posting a request and if the operator is not in a state used 
to set the function. If the operator is setting the function, the LED is 
already on and is not flashed. 
The Module Delay-Routine Delay routine provides a software waitloop style 
of delay routine used mainly during powerup. 
The Module DELTIME-Routines ADELTIME DELTIME routines are used to determine 
the interval between the current time and the specified time. DELTIME 
determines the time that has elapsed since the specified time while 
ADELTIME determines the time that remains until the specified time 
arrives. 
The Display module contains routines that convert values into displayable 
messages and a routine that actually writes the messages to the display. 
Many of the routines have two entry points, DSPxxx and BFRxxx. The DSP 
version uses the standard buffer while the BFR version uses a 
user-specified buffer. The DSP version only will be described to avoid 
repetitive descriptions of the BFR versions. 
The DSPULZ routine is called to remove leading zeros from numeric messages. 
The DSPBCD routine is called to convert from a BCD value to a display 
image. 
The DSPOUT routine sends the message image to the display. 
The DSPTIM routine converts a time value into a message. 
The DSPTMP routine converts a temperature value into a message. 
The DSPERR routine converts an error number into an error message. 
The DSPPH routine converts a pH value into a message image. 
The EXTRAM module contains routines to support the NOVRAM image of the 
system configuration. 
The NVSUM routine is used to calculate the checksum value. It is used by 
the other routines to handle the checksummed configuration record. 
The NVUPDT routine is called whenever a change is made to the 
configuration. It updates the checksum value. Powerfail interrupts are 
masked until the new checksum has been completed. 
The ERTEST routine is called at powerup time to verify the system 
configuration. If the image is corrupted, it is reset to reasonable 
fallback values. 
The Filter module contains routines that allow the user to set the filter 
maintenance interval. It has already been described in the operator 
settings sections. 
The Flash module contains routines that support a consistent 2 hertz flash 
of LEDS, display, etc. 
The Flashdrive routine is called to drive the timebase for the flasher. It 
is called once per timer interrupt synch by the main program. 
The Flash routine returns a on/off flag to allow callers to determine if 
they should be setting or clearing their outputs to flash. 
The Float module contains several routines that provide operations on 
scaled integer values. 
The FPADD routine adds two scaled integer values. 
The FPMULT routine multiplies two scaled integer values. 
The FPRND routine rounds a floating point number to the nearest integer 
value. 
The Idle module contains routines that handle keyboard inputs and drive the 
display while the operator is not programming any of the system's 
features. The display is stepped through the current time, temperature, pH 
value (if installed) and errors (if any are present). 
The KBIDLE routine handles keyboard inputs. If either of the arrow keys are 
pressed, the resettable errors are cleared. This is an operator 
acknowledgement of current alarms. 
The GO SHOTOD routine is called as an entry state handler for the idle 
mode. It sets up to display the time and switches to the time of day 
state. 
The SHOTOD routine is called to display the current time of day. The 
refresh flag is ignored. When the timer expires, the state is switched to 
show temperature. 
The SHOTEMP routine is called to display the current spa temperature. The 
refresh flag is used to avoid flickering values when the current input is 
straddling values. When the timer expires, the show pH state is invoked. 
The SHOPH routine is called to display the pH value. If no pH probe is 
installed, control is passed to the error displayer. Like the temperature 
display, the refresh flag is used to avoid flickering displays. When the 
timer expires, the error display state is called. 
The ERRIDLE routine is called to display the errors. If no errors remain, 
the display time state is entered. If another error exists to be 
displayed, the value is displayed and the timer is restarted. 
The Keyboard module contains routines that support the keyboard inputs. 
Keyboard inputs are signaled when the key is pressed. Key inputs are 
represented by an array of bits that are set when a positive transition 
has been detected. Three keys (up, down and maintenance) provide bits that 
correspond to the release of the keys. The up and down keys provide for an 
autorepeat that starts after a half a second and repeat at a frequency of 
approximately three hertz. Key transitions in both directions (on and off) 
are debounced. 
The KBINT routine is called to initialize the keyboard image. It sets up 
the image such that keys that are pressed while the system powers up are 
ignored. Thus, a jammed key will not activate its corresponding function 
when the system started. 
The KBSCAN routine is called periodically by the timer interrupt handler to 
scan the keyboard inputs and update the keyboard input image. Transitions 
are accumulated until they are cleared by a separate routine. Rollover is 
handled as additive keys. Simultaneous keys are allowed and are handled by 
the individual state handlers individually as prioritized keyboard inputs. 
This routine provides all debouncing and autorepeat functions. 
The KBGET routine is called by the main program to poll for keyboard 
inputs. Only transitions are reported. Any key inputs are cleared and 
reported to the caller. 
The KBAUTO routine is called to see if either of the arrow keys are being 
held down to generate autorepeat inputs. The result of this function is 
used to determine if the screen should be flashed. If repeat keys are 
active, flashing is inhibited. 
The Module Learn-Routine Learn routine is called as part of the control 
manager. If the heater is heating, the temperature value is monitored. If 
the temperature raises through two successive degree transitions, the time 
that elapsed between those two events is examined. If the time is less 
than one minute or two hours elapse before the event, a rate of change 
alarm is posted. Otherwise, the heating rate is stored for use in the spa 
ready function. 
The LEDS module contains routines that support the drive of the LEDs 
mounted inside the keypad. 
The LEDS routine is called to define the output state. All LEDs are 
redefined by this routine. They are lit or extinguished depending on the 
state of a corresponding bit. 
The LEDCLR routine is called to turn LEDs off. LEDs that have their 
corresponding bit set are turned off. Those whose bits are 0 are not 
affected. 
The LEDSET routine is called to turn LEDs on. LEDs that have their 
corresponding bit set are turned on. Those whose bits are 0 are not 
affected. 
The MAINT module controlling the maintenance mode has previously been 
described. It is implemented as two routines KBMAINT and DSPMAINT to 
handle keyboard inputs and display output respectively. While the main 
module views maintenance mode as one state, the maintenance mode is 
actually implemented as a set of substates in a manner identical to the 
state scheme used in the main module. 
The Module MYREGS-Routine MYREGS routine is called to determine the address 
of the current context's register set. The address of RO is returned in 
the accumulator. This routine is used when the registers are going to be 
used as general memory locations for subroutine parameters. 
The NOVRAM module contains routines which handle the special requirements 
of the NOVRAM. 
The NOVREAD routine is called to restore the nonvolatile image of the 
NOVRAM. It is called at powerup. It begins the restore function and 
handles the proper delay interval to give the NOVRAM to complete the 
refresh. 
The NOVWRITE routine is called by the powerfail interrupt handler to signal 
the storage of the system configuration image to the nonvolatile image of 
the NOVRAM. It guarantees that the cycle is completed and returns to the 
powerfail handler. 
The Module POWRFAIL-Routine POWRFAIL routine is the powerfail interrupt 
handler and has previously been described. 
The Revision module provides for the display of the software revision 
and/or version. It will display different values for variants of the 
system software to distinguish between them. Once the system has been 
completed, it will be sealed, so this will provide a surefire way of 
verifying the software contents. 
The KBREV routine handles keyboard inputs while the revision is being 
displayed. It allows the user to step forward past this function since 
this function does nothing other than display the revision value. 
The DSPREV routine is called to display the revision. The revision message 
is a constant message. 
The Module ROMTEST-Routine ROMTEST routine is called at powerup to check 
the program ROM. It executes a simple data line test and reports failure 
if any errors are detected. 
The Module RTC routine contains routines that support the real time clock 
device. 
The RTCINIT routine is called at powerup to initialize the RTC and to 
verify that the time value makes sense. If it does, it is assumed to be 
correct. Otherwise, it is assumed that the time value was lost and the 
time is reset to twelve o-clock midnight. 
The RTCPOL routine is called by the timer interrupt to poll the RTC for 
updates. If any changes have occurred, the new time is stored in RAM for 
use elsewhere in the system and a signal is returned that it is time to 
handle the one second update. If any changes have been posted, the new 
value is written. 
The GETTOD routine is called by the system at large to fetch the current 
time of day. 
The PUTTOD routine is called by the system at large to post a new time of 
day. On the next poll with a second update, the new value will be written 
to the RTC by the routine RTCPOL above. 
The SCHEAT module contains the routines that allow the user to configure 
the scheduled heating function. This allows the user to redefine the 
heating hysteresis when the spa is unattended. The minimal hysteris value 
allowed is five degrees. The behavior of these routines has already been 
described. 
The SETREADY module contains routines that allow the user to configure the 
set spa ready function. The behavior of these routines has previously been 
described. 
The SHOWMEM module allows the user to display the contents of both classes 
of RAM. It is available only in maintenance mode. 
The KBCPU routine handles keyboard inputs and allows the user to select the 
display of CPU RAM contents or continue to the next operation. 
The DSPCPU routine displays the message "CPU" to indicate what operation 
can be selected. 
The KBCSH routine handles keyboard input while displaying CPU RAM. It 
allows the user to raise or lower the current location or exit this 
function. 
The DSPCSH routine displays the current CPU RAM address as well as the 
contents. 
The KBNRAM, DSPNRAM, KBNRSH, DSPNRSH routines are identical to the CPU RAM 
routines above except that they operate on the NOVRAM contents. 
The Module Start-Routine Reset routine handles the powerup reset. Its 
function has previously been described. 
The TEMPSET module allows the user to set the desired spa temperature 
setpoint. This setpoint may be overridden by the scheduled heating 
function if it is enabled and the spa becomes unattended. The operation of 
this function has previously been described. 
The TICK module contains routines that support slow realtime timers (in the 
order of seconds). 
The TICK routine is called when the RTC has updated its second. It updates 
several operating timers as well as the runtime timers used to measure 
usage intervals for maintenance purposes. 
The GETTMR routine is called to get the current value for an operating 
countdown timer. 
The PUTTMR routine is called to reset the current value for an operating 
countdown timer. 
The Module TIMEBIN-Routine TIMEBIN routine is called to convert from BCD 
hours/minutes to a binary value in minutes. 
The Module Timer-Routine Timer is the timer interrupt handler. Its behavior 
has previously been described. 
The TIMESET module contains routines that allow the user to set the current 
time of day. Their function has already been described. 
The Module UNMIL-Routine UNMIL routine converts from military twenty-four 
hour format (used internally) to twelve hour an/pm format (preferred by 
most users). 
The VECTORS module contains vectors that provide for the transfer among the 
two pairs of program segments. The thirteenth address line (A12) is 
manipulated as an output line in paired vector handlers to handoff control 
of the processor from one pair of the program segments to the other. The 
reset and interrupt vectors are also represented twice in this module to 
provide for interrupt handling from either pair of segments. This segment 
organization explains the discrepancies in how a particular subroutine is 
called from different modules. The difference is usually the fact that the 
two callers reside in different segments. 
It will be understood that these routines describe one embodiment of the 
system and can be modified without departing from the scope of the 
inventive concepts herein taught. 
FIG. 5 shows one possible configuration of the keyboard 48 for the spa 
control panel 12. The overlay on the spa control panel 12 contains lights 
and a series of push button switches which can be depressed to switch on 
the appropriate functions. Preferably, an audible tone alerts the user 
that the computer 10 has received the signal sent by depressing the key. 
The jet button 49 operates the high speed pump 24 for the jet action in 
the spa. After the jet button 49 is depressed, the system will shut off 
the pump 24 if there is no flow in the system after five minutes of 
operation. The user is notified of the malfunction by an error message 
shown on the display. In a preferred embodiment, the low speed pump 
automatically is operated when the heater is activated. By pressing the 
jet button 49, the high speed overrides the low speed pump in pump 49. The 
heater 26 is still operable but the heating efficiency decreases because 
the water is moving faster over the heating element (in 220 v, in 110 v 
high speed pump disables heater). Interlocks link the pump 24 to the 
heater 26 so that the pump 24 runs fifteen seconds before the heater 26 is 
turned on and runs sixty seconds after the heater 26 is turned off. This 
ensures fluid flow during operation of the heater 26 so that hot spots in 
the system are not allowed to accumulate. 
The air button 51 operates the blower motor (not shown) for the bubbling 
action in the spa (same interlock as jet/heater). The light button 53 
operates any lights installed in the spa. The up arrow button 55 and down 
arrow button 63 are used in conjunction with the set clock 57, set 
temperature 59, set ready 50, scheduled heating, and filter 61 buttons. 
The purpose of the up arrow button 55 is to increment data that is 
presented on the display 46. The down arrow button 63 is used in 
conjunction with these same buttons to decrement data that is presented on 
the display. The set clock button 57 is used to set the current time of 
day and is activated by pushing the set clock button 57. The desired time 
can then be set by activating the up arrow button 55 or the down arrow 
button 63. The set temperature button 65 can be used to control the 
temperature value for the thermostat in the heater 26. To set the 
temperature, the set temperature button 65 is depressed and the current 
setting for the thermostat will be shown on the display. The up arrow 
button 55 or the down arrow button 63 can be used to increase or decrease 
the temperature setting as desired. When the desired value is shown on the 
display 46, the set temperature button 65 is depressed and the system will 
revert to the normal scroll in display. The ranges on the temperature 
setting may range from 40 to 104 degrees Fahrenheit. 
Referring to FIG. 6, when the system is powered up, the system is reset 100 
by system initialization 102 which enables certain events and parameters 
and then calls the main program 100. Certain interrupts such as the timer 
interrupt 106 and the power fail interrupt 108 are enabled to detect 
future interrupts which can then be polled 100 or effect a system shutdown 
112. The powerup reset 100 also generally clears all RAM 32, turns off 
control outputs for devices 24, 26, 28, 30, initializes the real time 
clock 34 reading and the keyboard scanner, tests the NOVRAM 32 image for 
validity, and tests EPROM memory 44 (See FIG. 7). 
On power-up sequence, the AC line input is read and the system electronics 
make a determination on whether the power is 110 v or 220 v. This status 
is read through a digital input by microcomputer 10 and an associated flag 
is set in RAM indicating which power supply is connected to the 
controller. On 110 v, the following constraints are imposed by the 
software: 
Heater and low speed pump will be turned off if either the high speed pump 
(jets) or the blower is turned on. 
The heater LED will flash during this time indicating it is trying to heat 
but has been overridden. 
On 220 v systems, no constraints are applied. The operation of this 
function is illustrated in FIG. 8. 
The set ready button is used to preset the time and temperature that is 
desired by the user. 
The microcomputer 10 calculates the proper time to initiate heating based 
on the present initial temperature of the water, and the stored data on 
the rate of heating for the particular spa. Each time that the spa is 
heated, the microcomputer 10 monitors the rate of change in the water 
temperature and stores this information in the internal memory. This data 
is then used to calculate the time necessary to heat the spa water from 
the initial temperature to the selected temperature. 
To operate the set ready, or spa ready mode, the set ready button 50 is 
depressed and the set ready light 50 and the hours light digits on display 
46 are illuminated. The hours are set by using the up button 55 and down 
button 63 arrows. When the hours are correct, the set ready button 50 is 
depressed and the minutes digits will flash. The minutes data are set by 
using the up button 55 and down button 63 arrows. When the minutes data is 
correct, the set ready button 50 is depressed and the current thermostat 
setting is displayed. The up button 55 or down button 63 arrow is pressed 
to select the proper temperature. The set ready button 50 is then 
depressed again and "on" or "off" will flash on the display screen 46. 
This indicates whether the feature is enabled or not. The set ready button 
50 is again depressed and the data is entered. When it is time to begin 
the heating cycle, the system program LED on display 46 will flash to 
indicate that the feature is active. 
When the spa is heated to the proper temperature, the programmed thermostat 
setting becomes the current thermostat setting and the system will 
continue normal operation. 
If enough time is not allocated for the spa to reach the desired 
temperature, and time runs out before the heating process is normally 
completed, the programmed thermostat setting will become the current 
thermostat setting and the system will continue normal operation. 
The filtering button 67 allows the user to select the time for circulating 
the water in the spa for normal maintenance. To operate, the filter button 
67 is depressed and the hours digits and the filter light will be 
eliminated. The up button 55 or down button 63 is operated to select the 
hour, and the filter button 67 is depressed to set the new running time. 
The data is loaded into memory, the light next to filter button 67 will 
turn off and the display 46 will return to the normal scroll in operation. 
When the filter functions are active, the LED will flash. 
The use of the system is checked by determining whether any operator keys 
have been actuated within 30 minutes, or other selected interval, of the 
initial start time. If not, the high speed jet and turbo controls are 
turned off to conserve energy. 
The heating light 69 is illuminated when the heating element of heater 26 
is being activated. If the heating element is activated and the 
temperature of the water is not increasing, then an error message will be 
displayed. The LED will flash when the heater 26 is in a warm-up or 
cool-down cycle. 
The system may be diagnosed by operating a switch in the system 
innerconnection panel 14 to place the keyboard 54 in display in the 
diagnostics mode. By pressing the jet button 49, the total number of hours 
of operation on the pump 24 will be displayed. Pressing the air button 51 
will show the total hours of operation on the blower motor. Pressing the 
set temp button 59 will display the total hours of operation on the heater 
26 and will eliminate the set temp light. Pressing the set clock button 57 
will display the total hours the system exceeded the desired temperature, 
designated as greater than 104 degrees Fahrenheit in the preferred 
embodiment. The light associated with the set clock button 57 will be 
eliminated after any other button is pressed. Pressing the up arrow button 
55 or the down arrow button 63 will eliminate other modes and turn on all 
lights on the panel 54 and will turn on all segments of the display 46 
along with the colon. The normal operation of the system is disabled when 
the maintenance switch is on. For example, the lights, turbo and jet 
outputs, and heater are shut down when the system is in maintenance mode. 
The system may display error codes which show potential problems within the 
system. Typical error codes which may be displayed might include 
information showing that the heater 26 was not heating, the pump 24 was 
not operating, there was insufficient time to heat the spa to the desired 
temperature, there was no water flow in the system, or there was failure 
in the microcomputer 10. Sensors (not shown) can be located at select 
locations in the system. From these sensors, the system can check for 
frozen water in the system and can determine whether the pH reading of the 
system is outside of a desired range. The system provides two functions 
regarding freezing of the water in the system. First, if either 
temperature sensor reads a temperature of thirty-four degrees or lower, 
the spa is considered frozen and all operations are disabled. The heater, 
the pumps and the blower are disabled to avoid damage to the mechanisms. 
Second, if the heater temperature drops below thirty-eight degrees, an 
impending freeze is signaled. The reaction to this condition is to run the 
low speed pump for five minutes. If the condition has not improved, the 
heater is started. Every five minutes thereafter, the temperature is 
rechecked. If the condition clears (the temperature rises above forty 
degrees), operations return to normal. This feature operates in addition 
to and in parallel with other operating modes. 
This feature addresses the common problem of a spa being cooled by exterior 
cooler temperatures. The pipes and heater tend to cool faster since there 
is a small mass of water being cooled. If the pipes are allowed to freeze, 
they may be damaged or the moving mechanisms such as the pump or blower 
may be damaged when they are activated. 
In another embodiment of the invention, the system can monitor the 
temperature of the water at different locations in the system to determine 
whether there is blockage in the system. The spa system accomplishes this 
by monitoring the temperatures detected by sensors located at selected 
locations in the spa control system. In one embodiment of the invention, a 
first sensor (not shown), which can be a solid state sensor, is located 
upstream of the heating element at a selected location and a second sensor 
(not shown) is located downstream of the heating element. As water flows 
over the heating element of heater 26, the sensors detect the temperature 
of the water at the selected locations. The microcomputer 10 processes the 
signals generated by the sensors and calculates the difference in 
temperature between the values detected by the sensors. The microprocessor 
selectively activates and deactivates the heating element of heater 26 to 
control the rate of heating. If the difference exceeds a selected amount, 
a warning on digital display 46, or other warning such as an audible 
sound, can be generated to warn the user of a malfunction in the spa. This 
function of the invention is shown in FIG. 7. 
In one embodiment of the system, two temperature probes are monitored 
constantly for temperature differences whenever the pump is in operation. 
When the pump is started, five minutes are allowed for the two readings to 
get within six degrees Fahrenheit of one another. If the probes fail to 
match after this period, all spa operations cease and an error message is 
displayed to the user. If the heater temperature is more than six degrees 
higher than the spa temperature, the heater is not turned on. If the 
heater temperature is more than six degrees colder than the spa 
temperature and the heater function is signaled to be on by other portions 
of the control program, the heater is turned on even though the 
temperatures do not match. If at any time after the first five minutes the 
difference between the two temperature readings exceeds six degrees, all 
spa operations are disabled and an error message is displayed to the user. 
As previously noted, this embodiment determines whether flow is present in 
the spa plumbing. If a blockage exists, it will result in a temperature 
difference which will cause the system to halt operations. The initial 
five minute period allows for the equalization of temperature differences 
that naturally occur when no water flow is present. Typically, a finite 
period of time is required for plumbing fixtures to warm and cool and for 
the temperature sensor to react to its surroundings. 
In addition, the microcomputer 10 can calculate the rate of heating 
detected by either sensor to determine whether there may be fluid blockage 
in the spa system. This calculation can be performed by dividing the 
change in temperature by the change in time to compute the rate of 
heating. For example, if there is a fluid blockage in the system, the spa 
water surrounding the heating element of heater 26 may rapidly overheat to 
create a "hot spot" in the spa system. If the temperature of the water 
does not increase, there may be a malfunction in the heating element. If 
any error is detected which signifies that the spa system is not properly 
working, the microcomputer 10 can deactivate the heating element to 
prevent overheating of the components of the spa system or can signal an 
error code on the display. The rate of heating can also be monitored to 
ensure that scalding water is not unexpectedly circulated in contact with 
the spa user. A cumulative average rate of heating for the spa system can 
be calculated from the heating rates which are calculated each time that 
the spa temperature is increased. This function of the invention is shown 
in FIG. 9. 
In one embodiment of the invention, the temperature of the water can be 
maintained within a selected temperature range or hysteresis when the spa 
is unattended, and the system can be programmed to heat the water 
temperature to a selected amount at a desired time. This function, 
referred to as the scheduled heating function, is begun by setting the 
start time and the high and low temperature limits. Next, the function is 
enabled. For example, the operator might select a lower temperature range, 
while the spa is unattended, to conserve energy. A lower temperature range 
would also reduce the number of times that the spa system would cycle on 
and off to maintain the desired temperature, if the lower water 
temperature is closer to the ambient temperature. Conversely, the operator 
can select a higher temperature range, closer to the desired temperature 
of the spa water, to minimize the time required to heat the spa water to 
the selected operating temperature. The ability to control the temperature 
of the water while the spa is unattended also yields other useful 
benefits. For example, the spa system can be programmed to heat the water 
to a desired temperature at a time of day when electrical power rates are 
minimal. The heat loss of the spa system during periods when the spa is 
unattended, calculated from the time that the spa water is heated to the 
desired temperature, can be calculated to maximize the operating 
efficiency of the entire spa system. 
In another embodiment of the invention, the heating rate of the water can 
be monitored to calculate the estimated time necessary to raise the water 
temperature to a desired level, and to detect certain failures in the spa 
system. For example, a sudden increase in the water temperature at a 
specific point in the spa system may signal that there is a loss of water 
circulation. If a sensor detects a heating rate which exceeds a selected 
rate, a warning message may be displayed, or the heating element of heater 
26 or the entire spa system may be deactivated to prevent deleterious 
heating of the spa components. As previously set forth, the rate of 
heating, together with the actual temperature reading and volume of water 
in the spa system, can be used to calculate the time required to heat the 
spa water to a desired temperature. This information can be stored in the 
microcomputer to assist in predicting the time necessary to heat the spa 
water to the desired temperature, beginning with the initial temperature 
of the water when the spa is unattended. This function is shown in FIG. 
10. 
To further illustrate the spa control system and certain of its functions, 
FIG. 11 shows a flowchart for one embodiment of the system which 
illustrates Power-up/Reset function, which describes how the system is 
initiated and can be modified by one operator; FIG. 12 shows a flowchart 
for the Timer Interrupt function, which interrupts a programmed command; 
and FIG. 13 shows a flowchart for the Powerfail function, which shuts down 
certain components of the system upon a certain event. As with other 
embodiments illustrated herein, the flowcharts shown in FIGS. 11-13 
represent differing embodiments of the present invention and may be varied 
without departing from the scope of the invention. 
The embodiments shown above are merely illustrative of the present 
invention. Many other examples of the embodiments set forth above and 
other modifications to the spa control system may be made without 
departing from the scope of this invention. It is understood that the 
details shown herein are to be interpreted as illustrative and not in a 
limiting sense.