Transcript ECE 4591 * Design Workshop

Lecture 1:
Safety and Protection
1.
2.
3.
A robot may not injure a human being or,
through inaction, allow a human being to come
to harm.
A robot must obey the orders given to it by
human beings, except where such orders would
conflict with the First Law.
A robot must protect its own existence as long
as such protection does not conflict with the
First or Second Laws.
>> Isaac Asimov <<
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NEVER WORK HOT!
All Design Work must account for Human
Exposure to Electric Hazards (Idiot-Proof)
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Safe Design Practices include:
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Enclosing Electrical Components to avoid incidental
human contact
Providing a Discharge Path for all Capacitors
 Design for discharge to under 5V in 2 seconds
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Design for Environment
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Internal Cooling/Heating (entire exterior must be
“touchable”)
Weatherproofing
Hazardous Materials/Containment
 Battery Acid
 Lead
 Oil
Source: commons.wikimedia.org
Peltier Devices – Exploit the Thermoelectric Effect to
convert a temperature differential into an electric
voltage (Reversible!)
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Kill Switches
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Must completely De-Energize Project
If your project is mobile, it will require a Local Kill
Switch (Big RED Button, Easily Accessible)
Source: Cartek
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A remote Kill Switch could act via one of many
“wireless” technologies: Infra-Red, AM Radio,
FM Radio, IEEE 802.11g, Bluetooth, etc.
Range and Noise will be issues in the Contest
Environment
Example: http://www.kitsrus.com/pdf/k180.pdf
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UHF Radio
2-Channel (Control 2 things)
Relay Backend (Heavy Duty)
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Grounding too often an ‘Afterthought”
Soild, Reliable Ground Plane eliminates many
Noise and Reliability Problems
Ground Plane on Mobile Platform cannot
reliably be joined to Earth Ground. (Floating
with Respect to Earth) Induced Voltages on
Vehicle must be considered when designing
and maintaining Vehicle
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Good Example of Terminating a Ground Wire
(or any wire) – Be aware of Vibration!
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Proper Termination of Shielded Cable
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In the case where a low power analog signal
(such as from a radio antenna) requires a
ground plane, AVOID direct connection to a
ground plane used for digital equipment
(Noisy).
In the absence of Earth Ground, establish an
Analog Ground Plane and a Digital Ground
Plane and connect the two with a resistive path
to attenuate noise.
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Electrical Circuits Require Protection against
Fault, Failure or Improper Use
Always Know the Failure Modes of Equipment
used in your Design (e.g. A Diode can fail
short)
Types of Circuit Protection:
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Over Current
Over/Under Voltage
Over Heating
Over/Under Frequency (AC Systems)
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Since most circuit designs assume established
voltage levels within the circuit, regulating current
will regulate the power in the circuit.
Conductors must be sized to handle the maximum
load current and any transient short-circuit current
level available.
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Example: NEC indicates 14 Gauge Solid Copper will
safely carry 15 Amps when properly protected by a
circuit breaker
Know When to Use Solid Wire and When to Use
Braided Wire
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Circuit Breaker – Rated for a maximum
application voltage, interrupting level and
maximum interrupting current (or volt-amps)
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Fuses
Inexpensive Over Current Protection
 One – Shot
 Fast or Slow
 Be Aware
of resistance
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Self-Resetting Fuses
Thermistor that is conductive at room temperature
If current exceeds rating, heats up and becomes nonconductive
 Conductive again after cooling down
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Source: commons.wikimedia.org
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It is often desirable, especially in power
electronics, to limit transient over-voltages in a
circuit
Zener Diodes are an
inexpensive means of
limiting low-power
over-voltages
MOV (Metal-Oxide Varistor) Surge
Suppressors provide a heavier duty solution
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IMPORTANT to electrically isolate delicate
electronics from power circuits (Pulse Width
Modulation motor drives, etc)
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Provide Electric Isolation (energy transfer is
through magnetic circuit in core)
AC Signals ONLY
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Provide Electric Isolation (magnetic circuit)
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Provide “electro-mechanical Amplification”
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Low Power Signal Controls Large Power Circuit
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AC or DC
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Not for
Repetitive
Operations
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Provide Electric Isolation (Energy Transfer via
Photons)
Many Types of Output: BJT, Darlington Pair,
SCR, etc
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Enable Pin = 0 puts driver in High Impedance
State (Open Circuit A to B)
High Input Z, Low Output Z (10 GE output)
Non-Inverting or Inverting