How to test input resistance
The input impedance of an electrical network is the measure of the opposition to current impedanceboth static resistance and dynamic reactanceinto the load network that is external to the electrical source. The source network is the portion of the network that transmits power, and the load network is the portion of the network that consumes power.
If the load network were replaced by a device with an output impedance equal to the input impedance of the load network equivalent circuitthe characteristics of the source-load network would be the same from the perspective of the connection point. So, the voltage across, and the current through, the input terminals would be identical to the chosen load network. Therefore, the input impedance of the load and the output impedance of the source determine how the source current and voltage change.
If one were to create a circuit with equivalent properties across the input terminals by placing the input impedance across the load of the circuit and the output impedance in series with the signal source, Ohm's law could be used to calculate the transfer function.
The values of the input and output impedance are often used to evaluate the electrical efficiency of networks by breaking them up into multiple stages and evaluating the efficiency of the interaction between each stage independently.
In this case. In AC circuits carrying powerthe losses due to the reactive component of the impedance can be significant. These losses manifest themselves in a phenomenon called phase imbalance, where the current is out of phase lagging behind or ahead with the voltage.
Therefore, the product of the current and the voltage is less than what it would be if the current and voltage were in phase.
With DC sources, reactive circuits have no impact, therefore power factor correction is not necessary. For a circuit to be modeled with an ideal source, output impedance, and input impedance; the circuit's input reactance can be sized to be the negative of the output reactance at the source.
In this scenario the reactive component of the input impedance cancels the reactive component of the output impedance at the source. The resulting equivalent circuit is purely resistive in nature, and there are no losses due to phase imbalance in the source or the load. The condition of maximum power transfer states that for a given source maximum power will be transferred when the resistance of the source is equal to the resistance of the load and the power factor is corrected by canceling out the reactance.
When this occurs the circuit is said to be complex conjugate matched to the signals impedance. Note this only maximizes the power transfer, not the efficiency of the circuit. This can create standing waves on the transmission line. To minimize reflections, the characteristic impedance of the transmission line and the impedance of the load circuit have to be equal or "matched".
If the impedance matches, the connection is known as a matched connectionand the process of correcting an impedance mismatch is called impedance matching. Since the characteristic impedance for a homogeneous transmission line is based on geometry alone and is therefore constant, and the load impedance can be measured independently, the matching condition holds regardless of the placement of the load before or after the transmission line.
In modern signal processingdevices, such as operational amplifiersare designed to have an input impedance several orders of magnitude higher than the output impedance of the source device connected to that input.Measuring resistances is similar to measuring voltages, with a key difference:. You must first disconnect all voltage sources from the circuit whose resistance you want to measure. Otherwise, pick the largest range available on your meter. Analog meters must first be calibrated before they can give an accurate resistance measurement.
To calibrate an analog meter, touch the two meter leads together. Touch the meter leads to the two points in the circuit for which you wish to measure resistance. For example, to measure the resistance of the resistor, touch the meter leads to the two leads of the resistor. Some components such as diodes pass current better in one direction than in the other.
In that case, the direction of the current does matter. But in circuits where it does, you can use the ohmmeter function of your multimeter to determine the exact value of a particular resistor.
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up. How should I calculate it? EDIT: If ideal op. By rule 2, no current flows into that input.
This lets us calculate the equivalent input resistance:.
Your second circuit is drawn incorrectly. You've connected R2 to one of the op amp's power pins, but it should be connected to the output. Here we need rule 1, which tells us that the voltage at the inverting input is equal to the voltage at the non-inverting input -- zero volts ground. We can work out the math, too:. Ideal op amps have infinite input resistance, and the voltage source is connected to only the input through Rs. This large input resistance is even drastically enlarged due to the feedback effect voltage feedback.
The situation, however, is different for the second circuit inverting amplifier.
How to Check Coil Packs With a Voltage Meter
Now we have current feedback - and the input resistance referred to the opamp input pin is decreased due to the feedback effect decreased by the large loop gain factor and can be neglected if in series with Rs. Hence, the remaining input resistance as seen by Vs is only Rs. Another explanation: For large values of the open-loop gain Ao usually 1E Hence, we assume that the node voltage at the inv. Rs is probably meant to be the source resistance.
It is a property of internal to the voltage generator.A faulty coil may fire intermittently, produce a weak spark or kill a cylinder completely.
Coils are sensitive to heat and may produce an intermittent problem if their internal components become weak.
Once the winding inside weakens or breaks, the problem is irreversible. However, you can test the coil pack on your car using a voltmeter. Locate the coil pack in your engine by following the spark plug wires from the spark plugs; the wires are connected to the coil pack. Depending on your particular vehicle model, you may find the coil pack mounted on one side or the back of the engine. Unplug the spark plug wires from the coil and label the wires if necessary for proper installation.
Unplug the pack's electrical connector and remove the coil pack from the engine, using a wrench or ratchet and socket if necessary. If your coil pack is mounted on the back of the engine, raise the front of the vehicle and safely support it on two jack stands to reach the coil pack from underneath the engine.
Set your ohmmeter to the ohms range. Turn on your meter and touch the spark plug wire terminals on one of the coils with the meter leads.
You may get a reading between to ohms, depending on your particular model. This checks the secondary resistance. You may get a reading between 0. This checks the primary resistance on each coil. Repeat steps 6 and 7 for each coil in the pack assembly, and compare your resistance readings to the specifications given on your vehicle service manual see "Tips". If your readings are out of range, replace the coil or coils as necessary. This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.
To submit your questions or ideas, or to simply learn more about It Still Works, contact us. Step 1 Park your car in a safe place and open the hood. Step 2 Locate the coil pack in your engine by following the spark plug wires from the spark plugs; the wires are connected to the coil pack. Step 3 Unplug the spark plug wires from the coil and label the wires if necessary for proper installation.
Step 4 Unplug the pack's electrical connector and remove the coil pack from the engine, using a wrench or ratchet and socket if necessary.
Step 5 Set your ohmmeter to the ohms range. Tip Consult your vehicle's service manual to obtain primary and secondary resistance specifications and identify primary and secondary terminals on the coil pack used on your car.
Items you will need Floor jack and 2 jack stands, if necessary Voltmeter. About the Author This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. Photo Credits under the hood image by Lucy Cherniak from Fotolia.Forgot your password? By Anderton June 20, Is your guitar sounding run down? Dull and anemic? It may not have the flu, but be feeding the wrong kind of input.
A guitar pickup puts out relatively weak signals, and the input it feeds can either coddle those signals or stomp on them. This is one piece of test equipment no guitarist should be without anyway, as you can test anything from whether your stage outlets are really putting out V to whether your cable is shorted. If theory scares you, skip ahead to the next subhead.
If you can, though, stay tuned since impedance crops up a lot if you work with electronic devices. Impedance is a pretty complex subject, but we can just hit the highlights for the purposes of this article.
The lower the resistance to ground, the greater the amount of signal that gets shunted. If you draw an equivalent circuit for these two resistances, it looks suspiciously like the schematic for a volume control Fig.
Conversely, a high guitar output impedance and low amp input impedance creates a lot of loss. Thus, low frequency signals may not be attenuated that much, but high frequencies could get clobbered. Buffer boards and on-board preamps can turn the guitar output into a low impedance output for all frequencies, but many devices are already designed to handle guitars, so adding anything else would be redundant.
Hence, the following test. This test takes advantage of the fact that impedance and resistance are, at least for this application, roughly equivalent.
Wire up the test jig in Fig. Plug in the signal generator and amplifier or other device being testedthen perform the following steps. Test points are marked in blue. You may later need to switch to a more sensitive range e. Measure the signal generator level by clipping the VOM leads to test points 1 and 2. Try for a signal generator level between 1 and 2 volts AC but be careful not to overload the effect and cause clipping.
Set the VOM to measure ohms, then clip the leads to test points 1 and 3. This will essentially equal the input impedance of the device being tested. The range of k to k is acceptable although you may hear some dulling. An input impedance over k means the designer either knows what guitarists want, or got lucky. Note, however, that more is not always better.
Input impedances above approximately 1 megohm are often more prone to picking up radio frequency interference and noise, without offering much of a sonic advantage.A vehicle speed sensor is a permanent magnet generator attached to the transmission under the vehicle. The sensor monitors several different engine and transmission functions and sends the information to the on-board computer.GATE 2005 ECE Input resistance of an amplifier using OP-AMP
It is triggered by the turning of the transmission shaft, sending a signal which increases or decreases in frequency with the vehicle's speed. This information is then relayed to the speedometer. If you suspect you have a problem with the speed sensor in your vehicle, you can check its operation with the help of a voltmeter. Raise the front of the vehicle and then set it down to rest securely on jack stands.
Chock the rear wheel to prevent movement. Locate the speed sensor attached to the rear section of the transmission. Follow the wire from the sensor and disconnect it from the wiring harness where it is attached to the frame. With the ignition on but the engine not running, push the probes of a voltmeter into the reference wires in the connector.
If no voltage is recorded, there may be a problem with the input signal from the on-board computer. Have the vehicle checked by a dealer service department. Reconnect the harness and turn the ignition off.
Remove the electrical connector from the speed sensor, and then remove the bolt that secures the sensor to the transmission housing.
Gently withdraw the sensor from the transmission. Place the sensor on a bench and check the pulsing AC voltage with the voltmeter as you slowly turn the gear by hand. If there is no voltage, the sensor may be defective. Install the new sensor into the transmission and replace the retaining bolt. Connect the electrical terminal and then test the new speed sensor by starting the engine.
If the sensor is operating correctly the "Check Engine" light should no longer be illuminated. This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Works, contact us.
Step 1 Raise the front of the vehicle and then set it down to rest securely on jack stands. Step 2 Follow the wire from the sensor and disconnect it from the wiring harness where it is attached to the frame.April 7, References Approved. This article was co-authored by Bess Ruff, MA. She has conducted survey work for marine spatial planning projects in the Caribbean and provided research support as a graduate fellow for the Sustainable Fisheries Group.
There are 15 references cited in this article, which can be found at the bottom of the page. This article has been viewedtimes. Impedance is the opposition of a circuit to alternating current.
It's measured in ohms. To calculate impedance, you must know the value of all resistors and the impedance of all inductors and capacitors, which offer varying amounts of opposition to the current depending on how the current is changing in strength, speed, and direction. You can calculate impedance using a simple mathematical formula.
To calculate impedance, calculate the resistance and reactance of the circuit, then label resistance as R and reactance as X. Square both R and X, and add the two products together. Take the square root of the sum of the squares of R and X to get impedance. Display the answer in ohms. To learn how to calculate resistance and reactance, read on! Did this summary help you?
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