Download EET420-FinalReport - Department of Applied Engineering

California University of Pennsylvania
Department of Applied Engineering & Technology
Electrical Engineering Technology
EET 420
Instrumentation Design II
Final Report
Smart Coffee Bean Roaster
Fall 2008
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December 4,2008
Table of Contents
page #
Description
Theory
Technologies Used
Thermocouple
Transformer/Rectifier
LabView
Functional Specifications
Concepts of improvement
Details of Device
Ethical Impact
Appendices
Flowchart
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Description:
Problem:
The art of roasting coffee is a time consuming venture. The roast itself involves several tedious
steps:
These cycles must be carefully monitored to produce a well roasted bean. The cycle times are based on
the type of bean and the roast desired. For a single variety of bean there can be more than a handful of
roasting recipes. So either spend a good quantity of time watching your roasts, spend too much money
on a less than configurable roaster, or develop your own smart roaster.
Issues of Concern:
1. Variable AC voltage must be controlled to be uniform(lab conditions are nominal)
2. 4 phases of roast must be controlled
3. Due to heating element and chance of Fire, Safety feature should be considered
Solution:
Develop a system that controls roast recipes for any variety of roasts, taking the time out
of time-consuming so that the user is left with more consuming.
System Design:
Chosen design:
The system is an aggregate of Temperature control, Timing control, Power control, and
Roast control. Temperature control involves the use of a J-Type thermocouple to acquire ambient
temperature of the roasting chamber. Timing control utilizes software to control the timing of
each phase of the roast. Power control is three part, each using relays to apply power to the
System, to the Load (heating element and blower), and blower using the DC line from the step
down transformer for two states on and off. The Roast control uses software to prompt user for
type of Roast.
Alternate design:
The use of a blower with the ability to use pulse width modification was also an option.
Through this design an optocoupler with a diac is used to control a triac. This is done by using
pulse width to control the firing of the triac and subsequently the speed of the blower, which in
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turn controls the temperature of the roast. Due to the difficulty of removing the original blower
from the unit this design wasn’t chosen.
Theory:
The AC voltage from the outlet must be stepped down through a transformer. It then must be
converted to DC through a rectifier circuit prior to being sent to Labview software. Due to the
fact that the blower of the Poppery unit can’t be controlled by pulse width, and since it is
affected by the heating element being shut down, it’s voltage must be controlled independently
with respect to the heating element when the heating element is shut down. Three relays are to be
used to control these conditions.
4 Phases of bean roast – the phases will be controlled using a thermistor for temperature and
predefined time intervals to produce the desired roast.
Safety feature – tilt monitoring or temperature monitoring will be the focus of the safety feature.
Technologies Used
The use of a type J thermocouple as the main component for ambient temperature acquisition is
one proposal and will be located within another subsystems sensor.
A thermocouple consists of two dissimilar metals joined together at one end but open at the
opposite side. Heat at the short-circuited junction produces a small dc voltage across the open
ends, which can be connected to a meter for detection. There are different types of
thermocouples which are categorized by the metals used in their design. As shown in appendix
A1 the materials used changes the operating range and gauge of material changes lifespan. The
junction produces a voltage in proportion to the difference in temperature between the measuring
junction and the reference junction. A reference table is used (appendix A2) in order to decipher
the voltage to temperature. Mathematical solution can be used to convert potential difference to
temperature. The DC component of the thermocouple output is digitized and displayed as body
temperature.
Usages of thermo couples can range from high temperature molten steel application to safety
features on home appliances. Advantages are low cost, high supply, and minimal implementation
effort. Disadvantages are lack of sensitivity over a small range.
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Transformer Rectifier
A transformer is a device that transfers electrical energy from one circuit to another through
inductively coupled electrical conductors. A changing current in the first circuit (the primary)
creates a changing magnetic field. This changing magnetic field induces a changing voltage in
the second circuit (the secondary). This effect is called mutual induction.
Changing AC to DC is done by electronic circuitry called a rectifier. It essentially chops off 1/2
of the AC current to make it similar to DC. Some of the lost AC current is turned into heat. That
is one reason your adapters sometimes get warm.
A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a
process known as rectification. Rectifiers have many uses including as components of power
supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum
tube diodes, mercury arc valves, and other components.
A full-wave rectifier converts the whole of the input waveform to one of constant polarity
(positive or negative) at its output. Full-wave rectification converts both polarities of the input
waveform to DC (direct current), and is more efficient. However, in a circuit with a non-center
tapped transformer, four diodes are required instead of the one needed for half-wave
rectification. (See semiconductors, diode). Four rectifiers arranged this way are called a diode
bridge or bridge rectifier:
For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (i.e.
anodes-to-anode or cathode-to-cathode) form a full-wave rectifier (in this case, the voltage is half
of that for the non-tapped bridge circuit above, and the diagram voltages are not to scale).
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LabVIEW
Figure 1 (First phase of flat sequence in LabVIEW)
Figure 1 is the first phase of the flat sequence in LabVIEW. As soon as the program is run, it
outputs to the front panel of the labview program a dialog box with the option to pick the type of
roast desired. The amount of time of roasting post crack is determined by this input, therefore
controlling the darkness of the roast.
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A
B
C
D
E
F
Figure 2 (Timing sequence of the roast in LabVIEW)
Figure 2 is the roasting portion of the flat sequence. This follows directly after the first phase
(Figure 1) of the flat sequence. All phases in the sequence move to the next phase after the
amount of time specified for each phase is complete. All phases also output to the dialog box on
the front panel the name of each phase during it’s duration. In phase A (off), all power to the
system is off for 2 seconds. In phase B (warm up), the power to all systems is on for 4 minutes.
In phase C (pre-crack), the power to all systems is on for 5 minutes. In phase D (post-crack), the
power to all systems is on, but the amount of time is varied depending upon which type of roast
(Figure 1) has been selected. In phase E (cooling), the power to the load (heating element) is
turned off and the power to the blower and the rest of the system is left on. This phase lasts for 5
minutes. In the final phase F (off), all power is turned off, and the program exits the sequence
after 5 seconds.
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Figure 3 (Thermocouple input and conversion to Fahrenheit degrees in LabVIEW)
Figure 3 shows the thermocouple temperature acquisition in labview. The voltages inputted
into LabVIEW are converted by the DAQ assistant into degrees Celsius. The temperature is then
converted into degrees Fahrenheit and outputted to the front panel of the LabVIEW program.
The thermocouple circuit is inside a while loop that starts and stops with the program executions.
Figure 4 (Power control to system, transformer, and load in LabVIEW)
Figure 4 is the LabVIEW while loop that controls the power to the coffee roaster. Three
separate DAQ assistants were used to output the appropriate responses to three relays that control
power to the system, transformer, and load. These power systems are dependent upon which
phase of the roast the flat sequence (Figure 2) is in. Doing so allows for both the blower and
heating element to run together, and also for the blower to run by itself during the cooling phase.
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Functional Specifications
Unit is driven by a 120 VAC outlet
Stepdown transformer 12to1 DC is used as a source
A rectifier circuit is used to convert AC voltage to DC voltage
LabVIEW handles input from thermistor and displays temperature
LabVIEW will be programmed to monitor temperature and time at predefined phases.
LabVIEW will control power to the heating element and fan, so that each phase is completed
successfully.
Concepts of Improvement
The utilization of LabVIEW to send a pulse width controlled TTL signal to a power
control unit in an effort to control the AC voltage to the heating element. LabVIEW would read
the already designed temperature acquisition unit. This data would then be compared to set
points during each phase of the roast. Based on the comparison the pulse width of the TTL signal
would correspond to the adjustments needed to produce the proper temperature, completing the
closed loop heat control system.
The use of a tilt sensor to detect when the device has tipped over and to shut down power
to prevent a possible fire. The sensor sends out a voltage when it isn’t tilted, and it sends a 0
when it is tilted.
Technologies need for Improvements
Triac
A triac is an electronic component approximately equivalent to two silicon-controlled rectifiers
(SCRs/thyristors) joined in inverse parallel (paralleled but with the polarity reversed) and with
their gates connected together. Formal name for a TRIAC is bidirectional triode thyristor. This
results in a bidirectional electronic switch which can conduct current in either direction when it
is triggered. It can be triggered by either a positive or a negative voltage being applied to its gate
electrode. Once triggered, the device continues to conduct until the current through it drops
below a certain threshold value, such as at the end of a half-cycle of alternating current (AC)
mains power. This makes the TRIAC a very convenient switch for AC circuits, allowing the
control of very large power flows with milliampere-scale control currents. In addition, applying a
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trigger pulse at a controllable point in an AC cycle allows one to control the percentage of
current that flows through the TRIAC to the load (phase control).
Optocoupler
An optocoupler is a device that uses a short optical transmission path to transfer a signal between
elements of a circuit, typically a transmitter and a receiver, while keeping them electrically isolated —
since the signal goes from an electrical signal to an optical signal back to an electrical signal, electrical
contact along the path is broken.
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Inductive Load With Nonsensitive-Gate Triac
Details of Device:
Tests performed as for now have determined the max temperature under normal conditions with
no voltage control to be 385 degrees Fahrenheit.
Roast should consist phases
Off
Warm-up
Pre Crack Roast
Post Crack Roast
Cooling
Off
Ethical Impact
It has been determined that there is no negative ethical impact from this design. The
device should aid in coffee roasting hobbyist in there pursuit of the perfect roast.
Appendices
Gantt Chart
Circuits
Flow Chart
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Task
Section Number
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2
3
4
5
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10/23 10/25 10/27 10/29 11/3 11/8 11/11 11/16 11/19 11/24 11/28 12/1 12/3
Proposal Abstract
1 - a. Draft 1 proposal
b. Revised proposal &
Presentation
2 - Preliminary Design
3 - Identify/ order parts
4- Web Page Desing
5- Interim Report & Pres.
DC Acquisition Circuit: DC Monitoring for Power Driver Circuit
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