Sensors Flashcards
What is a Capacitive Sensor?
Capacitive proximity sensors are non-contact devices that can detect the presence or absence of virtually any object regardless of material. They utilize the electrical property of capacitance and the change of capacitance based on a change in the electrical field around the active face of the sensor.
What is a infrared sensor?
A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors.
What is sensitivity?
It can also be called as the transfer function of a process. It is the ratio between the change in the output of an instrument to the corresponding change in the measured variable. For a good instrument or process, the sensitivity should always be high, thus producing higher output amplitudes.
What is Piezoelectro effect?
Piezoelectro effect is the ability of certain materials to generate an electric charge in response to applied mechanical stress
What is voltage?
- Voltage is also referred to as a potential difference
- To get electrical current to flow from one point to another, a voltage must exist between the two points
What are the pros and cons of thermocouples?
What is a thermistor? and which two types are there?
A thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors
- With NTC thermistors, resistance decreases as temperature rises. An NTC is commonly used as a temperature sensor, or in parallel with a circuit as an inrush current limiter.
- With PTC thermistors, resistance increases as temperature rises. PTC thermistors are commonly installed in series with a circuit, and used to protect against overcurrent conditions, as resettable fuses.
What is the differences between a step-up and step-down transformer?
The first coil has more turns on the primary than the secondary in a step-down. And the secondary voltage is smaller than the primary.
Step-up more turns on the primary
Bigger voltage on the secondary
What is electrical resistance?
Resistance is an electrical quantity that measures how the device or material reduces the electric current flow through it.
The resistance is measured in units of ohms (Ω).
If we make an analogy to water flow in pipes, the resistance is bigger when the pipe is thinner, so the water flow is decreased
What are the equation for power?
What does Ohm’s Law say? And was is the formula?
Calculate power
The turns ratio is n1/n2 = 90/2250 = 0.04
120/x = 90/2250
x = 3300
What are the differences between photoelectric and proximity sensors?
What is a semiconductor?
Semiconductor: is a material that conducts current, but only partly
The conductivity of a semiconductor is somewhere between of an INSULATOR and CONDUCTOR
How does a location sensor work?
Ohms law example
What is signal processing?
Is an enabling technology that includes the fundamental theory, applications, algorithms, and implementations of processing or transferring information.
Signal processing is concerned with improving the quality of the signal
What does the Kirchoffs voltage law say?
The directed sum of the potential differences (voltages) around any closed loop is zero
What is accuracy?
It is defined as the difference between the indicated value and the actual value. The actual value may be a known standard and accuracy is obtained by comparing it with the obtained value. If the difference is small accuracy is high and vice versa. Accuracy depends on several other parameters like hysteresis, linearity, sensitivity, offset, drift and so on. It is usually expressed as a percentage of span, percentage of reading or even absolute value. The standard value is set by the government so as to maintain the standard.
What are the pros and cons of thermistor?
What is resistivity?
Electrical resistivity and its converse, electrical conductivity, is a fundamental property of a material that quantifies how strongly it resists or conducts the flow of electric current. A low resistivity indicates a material that readily allows the flow of electric current. Resistivity is commonly represented by the Greek letter ρ (rho).
What is inductance?
An inductor is an electronic component consisting of a coil of wire with an electric current running through it, creating a magnetic field. The unit for inductance is the henry (H). One henry is the amount of inductance that is required to induce 1 volt of electromotive force (the electrical pressure from an energy source) when the current is changing at 1 ampere per second.
What is the current in this circuit?
0.5A
What is a threshold?
Minimum level needs to reach before the change in the instrument output reading is of large enough magnitude to be detectable
What is electrical charge?
Electric current is the flow of electric charge through an object, which produces no net loss or gain of electric charge. The most common charge carriers are the positively charged protonand the negatively charged electron. The movement of any of these charged particles constitutes an electric current. In many situations, it suffices to speak of the conventional currentwithout regard to whether it is carried by positive charges moving in the direction of the conventional current or by negative charges moving in the opposite direction. This macroscopic viewpoint is an approximation that simplifies electromagnetic concepts and calculations.
Simplify circuit
hahahah
Calculate power2
What is a proximity sensor?
Proximity sensors detect the presence or absence of objects using electromagnetic fields, light and sound
What can cause measurement errors?
Error = True value - Actual error
Systematic errors - Consistent and repeatable errors
Random errors - Unrepeatable, inconsistent errors
Human error
Calibration error
What is span?
It can be defined as the range of an instrument from the minimum to maximum scale value. In the case of a thermometer, its scale goes from −40°C to 100°C. Thus its span is 140°C. As said before accuracy is defined as a percentage of span. It is actually a deviation from true expressed as a percentage of the span.
What is a resistenance temperature detector?
An RTD (resistance temperature detector) is a temperature sensor that operates on the measurement principle that a material’s electrical resistance changes with temperature.
Applications
- Air conditioning and refrigeration servicing
- Furnace servicing
- Foodservice processing
- Medical research
- Textile production
What is digital signal?
Digital signal is a discrete-time signal for which not only the time but also the amplitude has discrete values
What is a resistance strain gauge?
What is a loop in a circuit?
A collection of branches that form a closed path returning to the same node without going through any other nodes or branches twice
It is step down - the second coil have less voltage
A) Turns ratio a= 2400/240 = 10
B)
P = U*I
100 kVA (power = V*A)
Is=100,000/240 = 416.67 A
Ip = Is/a =416,67/10 = 41.67 A
Magnitude of the load impedance
Zs = Vs/Is = 240/416.7 = 0.576 ohm
Zp = Vp/Ip = 2400/41.67 = 57.5954 ohm
What is a conductor?
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electrical current) in one or more directions. Materials made of metal are common electrical conductors. Electrical current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases.
What are some of the pros and cons of a RTD?
What is a filter?
Filters are circuits that are capable of passing signals within a band of frequencies while rejecting or blocking signals of frequencies outside this band
This property of filters is also called frequency selectivity
What is a passive instrument?
“Passive” just means that no components inside need to be powered.
Common passive components include resistors, capacitors, and most potentiometers (“pots”) like a volume knob.
What is a active instrument?
”Active” means is that some component inside requires power, either a battery or an external voltage source for working.
Examples of active components include transistors, LED lights, and op-amps or other IC chips.
How do you calibrate a sensor?
Comparing the output of the instrument, under test against the output of an instrument of known accuracy
How does a ultrasonic sensor work?
Emit a quick burst of ultrasound (50kHz), (human hearing 20Hz to 20 kHz)
Measure the elapsed time until the receiver indicates that an echo is detected
Like a bat and dolphins
Electric current
The total charge that passes through some cross-sectional area A per unit time.
What is a Photoelectric sensor?
Photoelectric sensor: is an equipment used to discover the distance, absence or presence of an object by using a light transmitter
All photoelectric sensors consist of a few of basic components
A transmitter light source (light emitting diode(LED), infrared LED, laser diode)
A receiver (photodiode or phototransistor) to detect emitted light
Supporting electronics designed to amplify the receiver signal
What is a Oscilloscope?
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages
What is capacitance?
Capacitance is the ability of a component or circuit to collect and store energy in the form of an electrical charge
What is electromotive force?
Also called emf (denoted and measured in volt), is the voltage developed by any source of electrical energy such as a battery or dynamo.
A source of emf is a device that uses chemical, mechanical or other energy to provide the potential difference necessary for electric current
What is Range?
Range can be defined as the measure of the instrument between the lowest and highest readings it can measure. A thermometer has a scale from −40°C to 100°C. Thus the range varies from −40°C to 100°C.
Why is linearity important?
1 input and 1 output
What are some of the difference in AC to DC?
- Amount of energy carried
- Frequency
- Direction
- Current
- Flow of electrons
etc.
What affects resistance?
What is analog signal?
is any continuous signal for which the time (variable) of the signal is a representation of some other time varying quantity
What is electrical current?
What is a insulator?
An electrical insulator is a material whose internal electric charges do not flow freely; very little electric current will flow through it under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.
What is a Signal amplification/Amplifier?
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal
It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude
An amplifier can either be a separate piece of equipment or an electrical circuit within another device
What is a signal?
Signal is defines as any physical quantity that varies with time, space or any other variables
Example of signals:
- Electrical signals, voltages and currents in circuit
- Acoustic signals, acoustic pressure(sound) over time
- Mechanical signals, traffic lights
- Video signals, intensity level of a pixel (camera, video) over time
What is resolution?
A lower limit on the magnitude of the change in the input that produces change in the output
There is a difference between accuracy and resolution
What is Repeatability?
Describes the closeness of output readings when the same input is applied repeatedly over a short period of time, with
- Same measurement conditions
- Same instrument and observer
- Same location
- Same maintenance conditions
What are thermocouples?
Thermocouples operate under the principle that a circuit made by connecting two dissimilar metals produces a measurable voltage when a temperature gradient is imposed between one end and the other
What does Kirchoffs current Law say?
This law states that, for any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node; or equivalently:
Pros and cons using a infrared sensor?
What is a optical sensor?
Electro-optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal. They are used in many industrial and consumer applications, for example:
- Lamps that turn on automatically in response to darkness
- Position sensors that activate when an object interrupts a light beam
- Flash detection, to synchronize one photographic flash to another
- Photoelectric sensors that detect the distance, absence, or presence of an object
What is a transformer?
A transformer is a static electrical device that transfers electrical energy between two or more circuits.
What is Nyquist-Shannon Sampling Theorem?
In order to ensure a faithful reconstruction, the original signal must be sampled at an appropriate rate as described in the sampling theorem
The sampling frequency should be at least twice the highest frequency contained in the signal Mathematical terms: fs ≥ 2fmax
What is a Inductive Proximity Sensor?
A high-frequency magnetic field is generated by coil L in the oscillation circuit. When a target approaches the magnetic field, an induction current (eddy current) flows in the target due to electromagnetic induction. As the target approaches the sensor, the induction current flow increases, which causes the load on the oscillation circuit to increase. Then, oscillation attenuates or stops. The sensor detects this change in the oscillation status with the amplitude detecting circuit, and outputs a detection signal.
