Operation Instruction Manual
WS-1500A
Precision PID Temperature Controller
*
Version 1.0
Auber Instruments
730 Culworth Manor
Alpharetta, GA 30022
770-569-8420
www.auberins.com
March 2008
Introduction
Thank you for purchasing the Auber WS series temperature controller. We sincerely
appreciate your decision and trust that our machine will meet your expectations in both
the quality of the result and the value of our product. While we are delighted that you may
be anxious to operate the controller for your project, a few minutes of your time reading
through this manual will only serve to enhance your experience in the months and years
ahead. In particular, we would urge you to read through the safety warnings below.
Although this plug-and-play controller is very easy to operate, the process involves high
temperature and high wattage appliances and your safety is paramount.
SAFETY WARNINGS
• This controller is designed only to be used with devices that have limited power
and their own thermal cut off protection, such as a thermostat or thermal fuse in
case of controller failure. Do not use it with a cook top or hot plate.
• Do not place any objects on the top of controller surface which is used to vent
excess heat during its operation.
• When open the cover of a rice cooker or slow cook that has been running for
extended period of time, the cover will carry a lot of condensation that can drip to
everywhere. Avoid drip the water over the controller.
• The maximum electric current this controller can handle is 15 ampere. For 120
volt ac in US and Canada, this limits the heater power to1800 watts. In addition, if
the heater power is more than 1400 watts, the volume of the pot is also limited to
less than 10 gallons (or 38 liters). Due to its compact size and the splash proof
design for kitchen applications, the controller has a limited ability to dissipate the
*
Patent pending
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heat generated by the internal solid state relay during the initial heat up. The initial
full power heat up process cannot be more than 90 minutes. If you have a pot that
is larger 5 gallons (19 litters), please read Appendix 1 “Managing the heat
generated by the controller”
• Always place the sensor in the controlled subject when the controller is on.
Before turning on the controller, please make sure the sensor is placed inside the
container to be controlled. Leaving the sensor outside of the solution will form an
open loop operation. If the sensor is left outside, controller will assume the
temperature is low even if the controlled subject is already very hot. The controller
will provide full power to the heater. It will not only overheat the controller, but also
damage your appliance, and even cause a fire.
• The power cord provided with controller is specially designed for high power
applications. Do not replace it with regular computer power cord.
• This controller is designed to control the devices recommended by Auber
Instruments only. Using it to control a not recommended device can be dangerous
and cause fire. Auber Instruments is not liable for damages caused by misuse of
the controller. If you are not sure the controller can be used, please contact Auber
Instruments before use.
• If an abnormal display or noise is observed, turn the controller off, unplug the
power cord and contact the manufacturer before using it again.
• Clean the controller only when it is cool and unplugged.
• Do not allow children to operate the controller.
FOOD SAFETY ISSUES
WS controller allows you to set your own temperature and time to cook. This is
nothing new when comparing it to using your own oven to cook. You are responsible
for your own food safety. It is beyond the scope of this guide to teach you how to cook
delicious sous-vide style dishes safely, but we can give you a few tips.
• When cooking sous-vide, unless you are a professional sous-vide cook, always
cook at above danger zone temperature (40ºF – 140ºF/4ºC – 60ºC).
• If you need to cook within danger zone temperature, always use the freshest
ingredients from reliable suppliers. Ingredients suitable for raw eating are safest
for sous-vide cooking.
• Unless you are a professional sous-vide cook with proper chilling equipment,
always consume your sous-vide dishes immediately or hold them at safe
temperature (minimum 140F/60C).
• When cooking bacteria hazardous foods like pork and poultry, always check core
temperature meeting minimum food safety temperature standards according to
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your local health department.
• If you don’t have proper food core temperature sensor probe, always cook at
desired core temperature setting for the duration as specified by reliable recipes
plus a safety factor of at least 25% longer. Cooking at core temperature setting,
food can never over-cook from a temperature perspective. Extra cooking time
after the core temperature is reached can only make the food safer and its texture
tender.
• If in doubt about the safety of the food, throw it out.
• Unless you are trained sous-vide cooking professional, always cook sous-vide
dishes for immediate consumption.
• Double cooking procedures using traditional techniques before or after sous-vide
cooking are good practices and can make your food safer and tastier.
Specifications
Input voltage: 100 to 240 VAC 50 /60 Hz
Output voltage: Same as the input.
Maximum Current: 15A.
Fuse Size: 15A Fast blow.
Controller Mode: PID, PI, PD or P.
Output switching device: Built-in optically isolated solid state relay with zero voltage
crossing switching.
Sensor tip dimensions: 5 mm diameter x 70 mm long.
Sensor cable length: 3 ft (915 mm)
Timer Range: 0.1 to 99.9 hours. It can be turned off by user
Temperature resolution: 1 °C or 1 °F
Temperature display unit: Celsius or Fahrenheit
Temperature control range: +5 °C (°F) from room temperature to 140 °C (284 °F)
Temperature accuracy: ±1°C (±2°F) < 65°C (149°F). ±1.5°C (±3°F)> 65°C (149°F)
Dimension: 6.5 x 3 x 5.2 inch (170 x 80 x 135 mm) W x H x D.
Weight: 1.6 lb (0.8 kg) without power cord.
Note, for international orders (except Canada), the input power cord is not included due
to its weight and different plug requirement. The controller has standard IEC 320 C13/14
socket. Users can use a power cord that meets the local standard to power it. Please
make sure the wire gauge can carry the maximum current required. In addition, an
adaptor that can convert the output socket (NEMA 5-15) to the socket of local standard is
needed.
Operating Instructions
1) Description of the controller.
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Fig 1. Front Panel
1) Parameter Window (LED) - for displaying temperature values and controller's
system parameters.
2) Temperature status indicator - In normal mode, this LED indicates the heater
status. When it is on (lit), the heater is powered. When it is off, the heater power is
off. When it is flashing, it means the heater is on and off intermittently to reduce
the power output.
3) SET Key - for showing current temperature settings, getting into parameters
setting mode and confirming various actions taken.
4) “+” Key - To increment displayed value.
5) “-“ Key - To decrement displayed value.
6) Time Key – Change the Parameter Window between current timer and
temperature values, when pressed.
7) Mode indicator, the small “dot” – if it is lit and flashing, the value displayed in the
Parameter Window is time, else it is temperature.
8) Timer status indicator- In normal mode, When “8)” is on and “7)” is flashing, LED
shows the time passed since the controller powered on. When it is off, the LED
shows the current temperature detected by the sensor probe
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Fig 2, Back Panel
2) Connecting and operating the controller
Fig 3. Typical connection between the controller and the heating device (in this example,
the cooker).
The connection of controller should be done in the following steps.
• Plug the temperature sensor to the back of the controller.
• Plug the power cord to the back of the controller and the other end to the power
outlet on the wall.
• Turn on the controller to make sure the controller powers up properly. The
temperature display is in the range expected. Then, turn off the controller.
• Plug the heater to the back of the controller. If the heater has a switch, put it in the
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off position. Put the sensor inside the container to be controlled.
• Turn on the controller.
• Turn on the heating device.
3) Setting the temperature.
Press SET key twice. Both 2) and 7) will start to flash. The LED shows the current
temperature setting. Use “+” and “-“ keys to change the setting. When finished, press the
SET again to confirm the change.
Note: the temperature setting will not be changed if SET is not pressed (confirmed). The
display will return to the normal display mode if no key is pressed within 3 seconds.
4) Switching the display between temperature and time.
This is done by pressing the Time Key (“6)”) once. When “8)” is on (lit) and “7)” is flashing
at the same time, LED is in timer mode and shows the actual time passed since the
controller was last powered on. When “8)” is off (not lit), LED is in temperature mode and
shows the current sensor temperature.
5) Setting the timer.
Press SET key once and release it, both 7) and 8) will start flashing. The LED shows the
current timer setting. Use “+” and “-“ key to change the timer setting. When finished,
press the SET again to confirm the change.
Note: the timer setting will not be changed if SET is not pressed (confirmed). The display
will return to the normal display mode if no key is pressed within 3 seconds.
Using the timer The timer can be used in two different ways.
a) Use it as timer. If you set the timer for 20 hours, the controller will stop sending power
to the cooker 20 hours after it is powered up. It will display “End” on the window and send
an audio beeping sound. Turning off the power and on again will reset the timer.
b) Use it as a clock. Instead of using the timer function, many users just use it as a clock
to find how long the food has been cooked. To use it as a clock, set the time longer than
you need to use, or, just leave it at the original 99.9 hr position. During the operation,
press the “time” button once will change the display from temperature of the pot to the
time that has elapsed since powered up. Press the “time” button again will change the
display back to temperature.
6) Tuning the controller
This controller is shipped with parameters set for commercial rice cooker. You can try to
use this setting for other cooking device also because the setting it suitable for a typical
slow response and balanced system. If you feel the performance is not ideal, you can try
to use the recommended PID parameters listed in Table 1. These are the parameter we
obtain from tuning the system manually. Fig 5 shows how to change them.
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Symbol P I d
Display
Commercial Rice cooker 180 700 40
Electric kettle, 1.5 liter 95 80 20
NESCO 18 quart Roaster 250 900 230
Home use rice cooker, 54 60 15
Home use rice cooker, wine fermentation. (PD
mode) Switch set at Warm position 17 0 40
Slow cooker, 7 quart 180 700 40
Slow cooker, 4 quart 54 60 15
Slow cooker, PD mode (low overshoot) 40 0 40
Bradley Smoker 70 800 200
P I d
Table 1. Recommended PID parameters that can be used as reference point.
Please note that the P value in table is in Fahrenheit unit. If the controller is using
Celsius unit, divide the P value by 1.8. If you switch from Fahrenheit display to
Celsius, the controller will automatically convert all the settings.
6.1 Auto-T une
The controller's most powerful feature is its ability to regulate virtually any cooker with
stable temperature control. For stable temperature control the controller requires two
things; (1) the controller must be set to the correct power level (see next section) and, (2)
that it must be tuned to the cooker being used. Tuning is the process that matches the
control characteristics of the controller to the heating characteristics of the cooker. The
controller is said to be tuned to the cooker when its memory is programmed with values
telling it how fast the cooker warms up, cools off, and how efficiently it transfers heat. For
example, consider the difference between a heat lamp and a hot plate. When electricity
is applied to a heat lamp it begins to heat instantaneously, and when it's turned off it
stops heating instantaneously. In contrast, a hot plate may take several minutes to begin
heating when electricity is applied and even longer to start cooling when electricity is
turned off. But, to do this it must be programmed with the time constants. Describing how
fast the heater heats when electricity is turned on and how fast it begins to cool when it's
turned off. These time constants are called the tuning parameters.
.
Every type of cooker has its own unique set of tuning parameters. For the controller to
heat with stability, it must have programmed with the tuning parameters for the cooker
currently being used.
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When Should the Controller be Tuned?
If your cooker is not listed in the Table 1 of our pre-selected cookers, or the PID
parameters we provided are not working for your liking, you can use the auto-tuning
function to let the controller to determine the PID parameters automatically. Auto-tuning
function (it’s often known as self-tuning) can automatically optimize the PID parameters
for your chosen cooking system. The auto-tuning function will heat up your cooker then
let it cool down. It will repeat this heat/cool cycle several times. Based on the response
time of the whole cooking system, the controller will calculate and set the PID
parameters for your cooker.
Figure 4
Before using the auto-tune function, you must set the cooking equipment up in the exact
configuration it will be used. For example, to tune a rice cooker, place the sensor in the
room temperature pot filled with water and plug the cooker into the controller. If the
cooker has its own thermostat or power control, turn both as high as they’ll go. Set the
controller to the appropriate power level (see next Section). Turn the controller and
cooker on, and then enter the desired set point temperature closed to your normal
cooking temperature.
To activate auto-tuning, just enter code 166 to get into the PID setting menu. Set AΓ to 1
then exit the menu (see Fig 5). The display will start to flash alternately between AΓ and
the current water bath temperature, which indicates auto-tuning is in progress. When the
display stops flashing, the auto-tuning is finished. Now, the newly calculated PID
parameters are set and are used for the system. The new parameters will store in the
memory even the power is off.
You should always write down your old PID parameters, before letting the controller to
perform auto-tuning. This way if something goes wrong, you can always go back to your
old PID parameters. The water amount in the pot should be the same volume as you
would have normally used. Basically, you must setup your cooking system close to your
actual cooking environment.
The duration of auto-tuning depends on how fast the system is responding to the heating
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and cooling cycle. If the temperature of the cooker takes a long time to drop -when
heater is off- the auto-tuning could be a very long tuning process. This is especially true
with a well insulated cooker. The auto-tuning should be able to tune most of your chosen
with fairly good result.
6.2 Manual Setting the PID parameter.
If you tried auto-tune and the parameter we provide but feel the performance is not ideal.
the following sections discuss the definition of these parameters and how to change
them.
• LCK. Parameter lock. This function is used to prevent user to change the critical
parameters by accident. User has to use the code 166 to access the parameter
setting menu.
• P. Proportional band. It is in 0.1 degree units. This parameter control the output of
the controller based on the difference between the measured and set temperature.
Larger the P number means the weaker the action (lower gain). e. g. If P=100, the
proportional band is 10 degree (100 x 0.1=10). When the sensor temperature is
10 degrees below the proportional band (10 degrees below the setting), the
controller will have 100% output. When the temperature is 5 degree below the set
point, the output is 50%. When the temperature is equal to the setting, the
controller will have 0% output (assuming integral and derivative functions are
turned off). This constant also affects both integral and derivative action. Smaller
P values will make the both integral and derivative action stronger. Please note
the value of the P is temperature unit sensitive. If you found an optimized P value
when operating the controller in Celsius, you need to multiply the P by 1.8 when
changing the temperature unit to Fahrenheit.
• I. Integral time. The unit is in seconds. This parameter controls the output of
controller based on the difference between the measured and set temperature
integrated with time. Integral action is used to eliminate temperature offset. Larger
number means slower action. e. g. assuming the difference between the
measured and set temperature is 2 degree and remain unchanged, the output will
increase continuously with time until it reaches 100%. When temperature
fluctuate regularly (system oscillating), increase the integral time. Decrease it if
the controller is taking too long to eliminate the temperature offset. When I=0, the
system becomes a PD controller.
• d. Derivative time. The unit is in seconds. Derivative action contributes the output
power based on the rate of temperature change. Derivative action can be used to
minimize the temperature overshoot by responding its rate of change. The larger
the number is, the faster the action will be. e.g. when the door of incubator is
opened, the temperature will drop at very high rate. The derivative action change
the controller output based on the rate of change rather than the net amount of
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change. This will allow the controller to act sooner. It will turn the heater to full
power before the temperature drops too much
• T, cycle rate. The unit is second. This unit determines how long for the controller
to calculate each action. This parameter should remain at 2 second for almost all
applications.
Fig 5. Code 166 Parameter setup flow chart
Press and hold SET key for 4 seconds until LED display “LCK”, then release the SET key.
The display will show “0”. To get into parameters setting mode, you need to key in the
pass code. Use “+” and “-“keys to adjust the display to 166 (which is the pass code) and
press SET. The LED will show “P” for a second and then its P setting value, Use “+” and
“-“ keys to change the setting. When finished, press the SET again to confirm the change.
The display will show the “I “ for a second and its I setting value next, use the same “P”
setting procedure to set the I value. When finished, press the SET again to confirm the
change. The display will show the “d” for a second and its value next. Use the same “P”
setting procedure to set the d value. When finished, press the SET again to confirm the
change. The next setting is AΓ, the auto-tune. Use “+” to set the value to 1 and press
SET will activate the auto-tune. The next setting is the “t” setting, use “-” and “+” to set
the cycle time value. This value should remain 2 for most application. After change the
PID parameter, the controller needs to be turned off and on again for the best result.
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7) Setting other system parameters
These are the parameters that normally do not need to be changed. The lock code to
access them is 155.
• SC, calibration offset. The parameter is used to make the input offset to
compensate the error produced by sensor. e.g. if the temperature displays 2.0 C
in ice water mixture, set SC=-2.0 will make the display to shown 0.0 degree.
• Out, Output power reduction. It is expressed as a percentage value. This
function will allow you to control the maximum output power delivered by the
heater in your cooker, for example, if you set Out=50 and your heater is 1000
watts, the output will use 50% of the 1000 watts as the full output. It thinks the
1000W heater as a 500W heater. When the PID algorithm determines 50% output
value, the actual power output will be 250 watts. This function can be used in two
situations.
1) When you have a very powerful heater and using a very small pot of water to
cook, for example, an 1800 watts heater with a one litter (1 qt) pot of water. The
heater is too powerful for the small water volume. The moment it is on, it releases
too much energy to cause the temperature to overshoot. Although it is still
possible to stabilize the temperature with proper PID parameters, it is much easier
to control if you limit the maximum output to 25%. Ideally, an optimized
temperature control system should consume about 25 % of the heater power at
set temperature (steady state), for example, if you found out that only 50 watts of
energy is needed to maintain the temperature at 60 C (141F), ideally you should
use only 200 watts heater for the job. Too much power will make the system over
react too quickly. Too little power will make the system too slow in response. By
using the OUt function, you can make the 1600 watts heater to act as a 200 watt
heater for stable temperature control.
2) When the cooker consumes more power than controller can handle, for
example, if you have a 15 A , 120V AC heater and your cooker contains more than
38 liter (10 gallon) of water. It might take more than 90 minutes of full power
heating for controller to heat up the pot. Long time of full power operation might
cause the controller to over heat. You can set the output to 80%. It will prevent the
controller from over heat by staying a full power too long. For details, please see
Appendix 1.
• C-F, Display unit setting. You can set the display either Celsius or Fahrenheit.
When changing the display unit, the temperature setting and P constant will be
automatically converted.
• TK, Timer setting. The timer function can be turned off by user.
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Fig 6. Code 155 Parameter setup flow chart
Press and hold SET key for 4 second until Parameter Window displayed “LCK”. Release
the SET. The display will show “0”. Use “+” and “-“ keys to adjust the display to 155
(another pass code) and press SET.
Setting the calibration offset. The parameter window will first show “SC “for a second
and then its value, Use “+” and “-“ keys to change the setting. When finished, press the
SET again to confirm the change. For example, if the temperature is 1 C too high during
calibration then use “-” to set the value to -1 to offset value.
Setting the output reduction. The parameter window will first show “OUt “for a second
and then its value, Use “+” and “-“ keys to change OUt value to your desired limit value
and press SET.
Setting Celsius (C) or Fahrenheit (F). When SET is pressed, the display will show “CF” and then its value of either “C” or “F”. Press “-” for C or “+” for F.
Turning Timer “OFF” or “ON”. When SET is pressed, the display will show “ry” and
then “1” or “0”. Press “-” for “0” (off) and “+” for “1” (on). Press SET will return to Normal
mode.
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Summary: Parameter and its initial setting.
Symbol Display Description Range Initial
P
I
d
AT
Τ
SC
Out
C-F
ΤΚ
SV Set temperature
Timer Timer (hour) 0-99.9 99.9
p
I
d
A
SC
C-F
Timer, 1=on, 0=off 1
Proportional band (in 0.1 degree) 0-600 180
Integral constant (second) 0-900 700
Derivative constant (second) 0-300 40
Auto-tune 0=off 1=on 0
Cycle rate (second) 1-100 2
Off set (degree) -20~+20 0
Output power reduction (%) 1-100 100
Temperature unit °C or °F °F
Table 2. List of control parameters and its initial settings
0-120°C,
32-248°F 140
Warranty
Auber Instruments warrants this controller to be free from defects in material and
workmanship for a period of one (1) year from the date of the original purchase when
utilized for normal household use, subject to the following conditions, exclusions and
exceptions. The sensor of the controller is warranted for 90 days.
If your appliance fails to operate properly while in use under normal household
conditions within the warranty period, return the complete appliance and accessories to
Auber Instruments
730 Culworth Manor
Alpharetta, GA 30022.
If the appliance is found by Auber Instruments to be defective in material or workmanship,
Auber Instruments will repair or replace it free of charge. A dated proof of purchase may
be required.
The liability of Auber Instruments is limited solely to the cost of the repair or replacement
of the unit at our discretion. This warranty does not cover normal wear of parts and does
not apply to any unit that has been tampered with or used for commercial purposes. This
limited warranty does not cover damage caused by misuse, abuse, negligent handling or
damage due to faulty packaging or mishandling in transit. This warranty does not cover
damage or defects caused by or resulting from damages from shipping or repairs,
service or alterations to the product or any of its parts which have been performed by a
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repairperson or facility not authorized by Auber Instruments.
This warranty is available to the original purchaser of the unit and excludes all other legal
and/or conventional warranties. The responsibility of Auber Instruments, if any, is limited
to the specific obligations expressly assumed by it under the terms of the limited warranty .
In no event is Auber Instruments liable for incidental or consequential damages of any
nature whatsoever. Some states/provinces do not permit the exclusion or limitation of
incidental or consequential damages and therefore the above may not apply to you.
This warranty gives you specific legal rights and you may also have other rights which
vary from state to state or province to province.
*Important: Carefully pack item to avoid damage in shipping. Be sure to include proof of
purchase date and to attach tag to item before packing with your name, complete
address and phone number with a note giving purchase information, model number and
what you believe is the problem with item. We recommend you insure the package (as
damage in shipping is not covered by your warranty). Mark the outside of your package
“ATTENTION CUSTOMER SERVICE”. We are constantly striving to improve our
products and therefore the specifications contained herein are subject to change without
notice.
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Appendix 1
Managing the heat generated by the controller
The heat dissipation of the controller is directly related to the electric current drawing
power of the heater. If your cooker consumes less than 12 ampere of current or your pot
is less than 5 gal (19 liters), you do not need to worry about the heat generated by the
controller.
Sometime, the AC current requirement might not be marked on the cooking appliance.
To find out how much current it will draw, divide the power (in wattage) by the line voltage,
for example, an 1800 watts 120V heater will draw 15 A. A 2000 watts 240 V heater will
draw 8.3 Ampere.
Why the heat becomes an issue?
The solid state relay (SSR) used in the controller is a critical component for the precision
temperature control. With SSR, the power can be switched at high speed with no noise
and no life time limitation. Compared with electromechanical relay, however, SSR has
one drawback. It generates heat when passing the current. SSR is made of
semiconductor that has a limited conductance. When passing current, the heat will be
produced from the resistance. Each ampere of current will produce about 1.3 watts of
heat. When 15 Amp is passing through the controller, 20 watt of heat is produced in the
controller. As more heat is produced, the temperature inside the controller will rise. If it
reaches to higher than 70 C, it can shorten the life or even damage some the
components in the controller. The temperature inside of the controller depends on the
amplitude of the current, how long the controller needs to run at full power and the
ambient temperature.
The heat is only an issue during the start of the heating when the heater is running at full
power. Once the temperature is close to the set point, the controller will probably need
less than 50% of the power to maintain the temperature. Since the heat is directly related
to the current passing the controller, the heat produced at steady state will be
insignificant and can be ignored.
When the heat becomes an issue?
This controller can run at 12 A continuously without worry of the temperature of the
controller. At 15A, the temperature of the controller will increase with time. The bottom of
the controller where the heat sink is located can rise by 63F (35 C) from ambient if
running at full power continuously for 90 minutes. For this reason we don’t recommend
running the controller at full power for more than 90 minutes. For 120 VAC, 15 A for 90
15
minute will provide enough energy to heat 10 gallon (38 liters) of water up by 108F (60 C).
If your have a pot that is bigger than 10 gallon and the heater is drawing 15 A, and you
need to raise the temperature by 108 F, you better use one of the methods mentioned
below to reduce the heat in the controller. Otherwise, you might damage the controller.
Please note that when the ambient temperature is hot, as it is often the case in some
commercial kitchens, the temperature of the controller will get hotter. This is because the
heat dissipation is mostly determined by the temperature gradient (the temperature
difference between the ambient and the controller) instead of absolute temperature of
the controller itself. If the controller reaches 50 C when the ambient is at 20C, it will reach
70 C when the ambient is at 40 C.
Solutions to reduce the heat stress on the controller.
1) Use hot water. If you fill the pot with hot water that has a temperature close to the set
temperature, the heat dissipation of the controller is not an issue. As we have mentioned,
once the temperature is close to the set point temperature, the controller starts to pulse
(PWM) the power. The effective current is much lower, making heat not an issue.
2) Limit maximum output power. If you set output reduction parameter to 80%, then, a 15
A heater will become a 12 A heater. It will take 25% longer time to heat up the pot, but the
controller will not over heat.
In addition to these solutions, following information will also help you to manage the heat.
Place the controller in right place. The SSR of Auber WS series controller is mounted in
the bottom of chassis. The chassis is made of 3 mm thick aluminum for good heat
dissipation. Do not cover the controller with any insulation. If you are running at 15 A with
a large pot, place the controller in a well ventilated area and tilt the instrument up with its
front leg will help it to remove the heat better. However, the tilted position might allow the
water to be collected at the back frame. Although the controller is splash proof, you
should avoid water to be dripped to the controller when open the lid of the cooker.
Increase the P value. This can only provide limited help for reducing the heat. P is the
proportional band. P=200 means the proportional band is 20.0 degrees. When the
temperature is raised to less than 20 degree from the set point temperature, the
controller will start to reduce the power sooner. But if the integration time is set to very
short, the controller might start to run at full power again soon.
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Appendix 2
Controlling the Temperature of Slow Cooker
For long duration sous-vide cooking, water bath temperature stability can be easily
achieved with a slow cooker. Almost any PID parameters’ settings will hold the set
temperature within one degree, if given enough time. However, the time needed for a
slow cooker to stabilize at the set temperature is sensitive to the settings of the PID
parameters. A slow cooker normally takes 1-2 hours to reach the set temperature from
a cold start; during this period a slight temperature overshoot is expected. If food
pouches are added to water bath at set temperature, you may need to wait another hour
for temperature to stabilize again. You may want to shorten this long stabilizing period by
using appropriate PID settings according to your applications.
We used two slow cookers for this study, a 4-quart 200 watt unit made by Crockpot, and
a 7-quart 400 watt unit made by Euro Prox. These two cookers represent the majority
of the slow cookers on the market.
Based on the temperature controlling method, we can classify the slow cooker control
method into two classes, PID and PD (when I=0, No I). We will discuss the advantages
and limitations of each method.
A) Proportional and Derivative (PD) control mode.
When I (Integral) action is removed (I=0), the temperature controller becomes a PD
controller. The advantage of PD control mode is that you can reduce the temperature
overshoot to a minimum. If the food pouches are placed in the cooker with water (hot or
cold) and ramped (heated) up together, you would observe no temperature overshoot.
This is really the best cooking approach. However, if you add the food pouches after the
temperature has reached (or is close) to the set point, this would make the cooker longer
time to stabilize. The PD control mode is very fast to reach set point from a cold or warm
start. It is very slow to stabilize the temperature when there is temperature disturbance
caused by sudden temperature drop (adding cold food pouches).
The following parameters worked well from our study.
Symbol P I d C-F
Display
P I d C-F
Slow cooker, 4 quart 40 0 40 °F
Slow cooker, 4 quart 17 0 40 °C
Slow cooker, 7 quart 40 0 40 °F
Slow cooker, 7 quart 17 0 40 °C
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Depending on the amount of water in the cooker, the performance may vary slightly. If
the temperature still overshoots too much, increase the P value. If the temperature
stabilizes one degree below the set point, reduce the P value.
Technical explanation
For people used to a conventional thermocouple or RTD sensor based PID controller,
they may think a PD controller can’t hold the temperature within one degree, because a
few degree temperature offset is needed for the controller to output enough power to
maintain stability. However, this is not true for a thermistor sensor based controller,
because a thermistor sensor is much more sensitive. A 0.3 degree offset is sufficient for
the controller sending enough power to maintain the temperature within one degree of
set point.
B) Proportional, Integral and Derivative (PID) mode.
The advantage of using the PID mode is fast action and no temperature offset (<1
degree) in long duration cooking. The disadvantage of PID mode is that there will be a
small temperature overshoot. Depending on the parameters used, the temperature may
oscillate several times before it settles to the set temperature. Because the very slow
response of the slow cooker, it is very difficult to not have any temperature overshoot
when PID mode is used. However, if you are making sous-vide and want to drop the food
pouches into the pot after temperature is close to the set point, this small temperature
overshoot actually will help the cooking and is preferred by many cooks. This is because
in most cases, the overshoot is not high enough and long enough to bring the food
temperature above the set point. It will help to bring the food temperature reach desired
temperature faster.
The following parameters worked well for our test.
Symbol P I d C-F
Display
P I d C-F
Slow cooker, 4 quart 54 60 15 °F
Slow cooker, 4 quart 30 60 15 °C
Slow cooker, 7 quart 180 700 40 °F
Slow cooker, 7 quart 100 700 40 °C
It should be noted that these parameters are not optimized if the amount of water in the
pot is different. In general, weaker parameters (i.e., higher P and I) should be used when
a larger mass is heated (except that the derivative action should be lower). Larger mass
has larger heat inertia, so it needs to be moved more slowly to control. For the derivative
action, strong action will reduce the overshoot. In terms of long term temperature
precision, the difference in these parameters will have very little effect.
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This study is preliminary. It will give you a guide on how to achieve a good stability
control. We will keep you
updated when better results are obtained from our tests or from our customers.
Appendix 3
Controlling the kettle for making French Press Coffee
1) Make sure the sensor is immersed in the kettle. If there is enough water, try to not let the
sensor tip touch the bottom for the best result. This can be done by bend the cable so that the
sensor hangs on the side wall without tip touching the bottom.
2) The sensor used is completely immersable and safe for food product. The cable is made of
virgin FEP. The sensor tip is sealed in stainless steel housing with proprietary medical grade
sealant that is certified by USP class VI test.
3) The variation of water volume in the kettle will affect the heating speed. It will also affect the
control quality. When the water volume is less than 0.5 liter, it might become difficult to control.
In that case, you need to reduce the output power as discussed in main manual. The
optimal PID constant for 1.5 liter and 0.5 litter is slight different. Here is the list.
Volume P I D
1.5 liter 95 80 20
0.5 liter 190 80 20
The P value in the table is for Fahrenheit. Divide it by 1.8 if Celsius is used. Please note the
difference in performance with these two sets of parameter is very small. You have to plot the
temperature response curve to see it. If you change the water volume all the time, you
don’t need to change the parameter. But if you always use the same amount of water, you
might want set the parameter for the volume you used. Basically, the difference is in the P
value. Use large value if volume is small, use smaller value if volume is large. Both sets of
parameter will work reasonably well for the whole range.
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