In the field of electrical engineering, we use the quantities potential difference (in Volts), the electric current (in Amperes) and the electric resistance (in Ohms). If we want to express the potential difference in SI units, we have to use 1V = 1 kg m2s-3A-1. In addition, there is an indicator on the screen that shows whether the temperature is stable or still changing.
What is the correct way of writing the equivalent value or R1 and R2 in series that represents the 5% tolerance. As we will see in Chapter 3, the equivalent resistance of two resistors in series is calculated as R1 + R2. How much power is being dissipated in such a cable over 50 km when the cable carries a current of 500A.
If the resistors in the circuit in Figure 4 are 0.5 W, what is the largest potential difference that can be placed across points A and B. Choose the theoretical resistors so that the current drawn by the battery is 1 mA when the voltage divider is not loaded.
4 NETWORK THEORY
- Kirchhoff’s laws
- Equivalent circuit of a power supply
- Norton and Thévenin source transformations Given the electronic networks of Figure 6 and
- Equivalent circuit of a battery
- Superposition Given the network of Figure 8
- The Wheatstone bridge
- Time dependent circuits
Draw the Thévenin equivalent circuit of this power supply and state the values of the elements used. Draw the Thévenin equivalence of Figure 6 (between nodes A and B) and state the values of the components. Draw the Thévenin equivalence of Figure 7 (between nodes A and B) and state the values of the components.
What is the % error we make when we measure the output voltage between node A and B of the circuit of Figure 7 with a non-ideal voltmeter that has an internal resistance of 1kΩ. The potential difference across the bulb is measured with an ideal voltmeter and appears to be 8,250 V. Because this appears to be a bit low for a 9V battery, the potential difference without the light bulb is also measured: this appears to be 8,500 V.
What is the final potential (after waiting for a long time) across the capacitor after the switch is closed. Starting with UC = 0V at t = 0 sec, what is the magnitude of the electric current immediately after the switch is closed.
5 BASIC SENSOR THEORY
- Terminology
- The transfer function of a Pt100
- A resistive sensor
- The candle-clock
Now consider this Pt100 to be placed in a voltage divider with an ideal 100Ω series resistor and an ideal 5V supply. What is the non-linearity over the 0°C to 100°C range of the sensor plus this simple readout method. A strain gauge is a resistive element whose resistance changes as a function of deflection or stretch.
Using Excel, draw a line through the measured points (using the least squares method) to determine the relationship between resistance and deflection. Assuming the light burns at a constant rate in a reproducible manner, we can place a linear scale along the light. With an experiment, we want to determine the relationship between the length of the burning candle (l) and the time (t).
6 SENSOR-ACTUATOR SYSTEMS
From sensor to knowledge
Differential measurements
A resistive measurement bridge for a strain gauge
How might an electronic circuit for measuring the difference between two parameters y1 and y2 look like. How can we minimize the error (cross-sensitivity) in the output signal due to temperature changes. The output of a resistive bridge is the difference between the voltage on the left branch and the right branch: this appears to be from -5mV to +5mV maximum when the bridge has a power supply of Us = 10V.
7 SIGNAL CONDITIONING AND SENSOR READ-OUT
The Wheatstone bridge
In other words: if the LDR changes by 1 ohm, how many volts will change on the voltmeter.
An LDR in a voltage divider
We want to remove the sunscreen when the light intensity is higher than 1000 lux, and we want to reapply it when the light falls below 100 lux.
Sensor characteristics of an NTC
What determines the (non)linearity between the relationship of the temperature with the output voltage Uout.
MASTER IN MANAGEMENT
Schmitt trigger
We have a signal as shown in Figure 19 that we want to detect whether it is “high” or. Therefore, we decide to make a circuit with a low-to-high decision level of 1.7V and a high-to-low transition level of 0.9V.
8 ADC AND DAC
AD conversion
Measurement of light intensity
A temperature measurement
9 BUS INTERFACES
Bus interfaces
10 ASSIGNMENT 1: THE POSITION SENSOR
First measurement – does it work?
Calibration curve
Analyzing
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Error estimation
Remove the paperclips, slide the paperclips, reinsert them and repeat the measurement at d = 2 cm. Can you see the nature of the error (is it just a 10% fluctuation, or is it constantly changing?).
Repeat calibration experiment
Analysis
11 ASSIGNMENT: STRAIN GAUGE TRANSDUCER
- First measurement - does it work?
- Read-out electronics
- The strain gauge The equation
- Bridge set-up Consider the bridge setup of Figure 25
- Half bridge setup
Make such a sensor by drawing a square of conductive carbon on one side of the plastic strip. The paper clips can be used to contact the strip to measure the resistance along the entire length. Note: LIGS University is not accredited by a nationally recognized accrediting agency listed by the US Secretary of Education.
How do you convert the change in R (so far probably measured with a multimeter) into a voltage for sampling with a 0-5V ADC. What is the length of the strain gauge for a width of 2.5 cm and a target resistance of 1MΩ. What should be the shape of the strain gauge: a straight bar or should we snake.
Assume that the full scale change in resistance due to strain is 1%, how much temperature change do we allow for 5% error. What is the ratio between the common mode signal on the UBridge pins and the differential mode signal. What happens to the UBridge connection with ΔR if our strain gauge is not R0 as intended (and like the other three resistors in the bridge) but if it is 20% higher.
If we make two "identical" strain gauges, and we place one in a mechanical location in tension as shown in Figure 26, and one in compression, we have some advantages.
12 ANSWERS
RTh can then be found by observing the circuit as a voltage divider as shown in Figure 29. In this case it is the standard deviation of the measured instantaneous candle length relative to the estimated length at that time using the fitted line. As an amplifier to measure a difference, the OpAmp differential amplifier of Appendix B of the book, or a dedicated one, can be used.
In practice, very high linearity is observed for small changes in meter resistance. In this case the sensitivity is positive because the output increases with increasing resistance of the LDR. When two decision levels are switched, the screen will be stuck on one of the sides.
As long as the temperature dependence of R2 is not equal to that of sensor R1, the voltage division still gives a change in voltage with temperature change, only smaller. Already today, SKF's innovative know-how is essential to the operation of a large proportion of the world's wind turbines. In a Schmitt trigger, one of the resistors that determines the decision level of the comparator is effectively moved into place.
And indeed, with 10 bits over a range of 5V, we find a resolution of 4.89mV which is better than 5mV. Nyquist's theorem states that a sampling rate is needed which is at least twice the highest frequency in the signal. A voltage divider can be used to convert the resistance temperature sensor value to a voltage. The value for R1 can be chosen in the middle of the sensor's operating range: 47kΩ for example.
It could be the resistance of the cables plus the contact resistance of the paperclip against the paper. Now we are allowed to say that the fitted linear approximation definitely fits within the error range of the measurements, again only for distances above 4 cm. The characterization (calibration) of the sensor as done in Figure 37, is repeated after all experiments from Table 4 have been done.
Bending up seems to give a much lower sensitivity: there is less deformation of the resistive layer than bending down. The bridge resistance values should be the same as the nominal value of the sensor.
