how to test a resistor

Complete the circuit by connecting a power supply of known voltage. It’s true that measuring components while they’re in the circuit can lead to skewed readings. Testing at the motor itself eliminates the possibility of confusion caused by complicated electronic blower controls found in Electronic Climate Control systems. Turn on the power supply and measure the time taken for the capacitor to charge to 63.2% of the supply voltage.For example, if the supply voltage is 12V, then 63.2% of this is around 7.6V. Refer to Ohm's law for reference. If the screen reads OL (overloaded) the range is set too low and needs to be increased to the next highest range. You can check the resistor resistance with an ohmmeter or digital multimeter. Thanks to all authors for creating a page that has been read 349,503 times. Other factors that can affect resistance readings: Foreign substances (dirt, solder flux, oil), body contact with the metal ends of the test leads, or parallel circuit paths. By signing up you are agreeing to receive emails according to our privacy policy. This article was co-authored by Bess Ruff, MA. How accurate a multimeter is depends on the model. If the needle swings to a value on the multimeter that’s between the bottom and the top of the range, that’s an indication of a valid reading. With the metallic band on the right, the first and second bands define the first two digits of the resistance value, and the third band defines how many zeroes follow the second digit. First, test for static resistance per above…should be exactly 3 ohms, otherwise, toss the ballast. You can technically use anything that conducts electricity, from a piece of aluminum foil to a pencil mark on a sheet of paper, to test your … To test your transistor, first clamp the black probe of a multimeter to the transistor’s base. The orientation doesn't matter, because resist… share | improve this question | follow | asked Feb 16 '11 at 22:12. endolith endolith. ", Unlock expert answers by supporting wikiHow, http://www.physicsclassroom.com/class/circuits/Lesson-3/Resistance, http://en-us.fluke.com/training/training-library/test-tools/digital-multimeters/how-to-measure-resistance.html, http://www.electronics-radio.com/articles/test-methods/meters/multimeter-resistance-measurement.php, https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter/measuring-resistance, consider supporting our work with a contribution to wikiHow. Your fingers do indeed absorb current from the circuit when using high-voltage multimeters. According to the part datasheet, the value should be 98 Ohms, this one … Bess Ruff is a Geography PhD student at Florida State University. If your multimeter (if that is what you are referring to) is showing 0, turn the range down. What are the color codes on electric resistors? Did you know you can read expert answers for this article? In addition to a resistance value, measured in ohms, it has a maximum power rating, measured in watts. Thankfully, testing the blower motor resistor is not that hard and in this tutorial I'll show you 4 different tests that will help you troubleshoot it and find out if it's bad (or not). How can you tell if your starting range is inaccurate when measuring resistance with an analog multimeter? A resistor is a standard electronic component that has a constant electrical resistance in a circuit. wikiHow is where trusted research and expert knowledge come together. Analog readers usually have a needle that will identify the measurement on a scale, while a digital reader will provide a numeric reading. A potentiometer is a type of variable (adjustable) resistor. Try again... Not exactly! However, these readings won’t necessarily be very useful to you. When the blower motor resistor fails on your GMC pickup or SUV, the blower motor will only work in one speed and in a few cases not at all. Nope! Low-end meters are usually accurate within 1 percent of the correct value. Re-test to make sure! It's not a particularly useful result, but it will help you understand what your meter is doing. Are there any analogue multimeters which use a potentiometer instead of a bank of resistance in measuring voltage? This article has been viewed 349,503 times. Exactly! She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. Then, touch the red probe to the emitter and read the display to see if the resistance is high or low. Only one of these answers is correct here! 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. One way to keep your hands off components is to attach them to a testing board, or "breadboard" when testing for resistance. She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. Potentiometers are widely used to control the output of electrical devices (e.g. Most multimeters inherently measure voltage, and pass a current to be measured through a shunt resistance, measuring the voltage developed across it. This article has given me a, "Simple, clear and concise. TechRepublic Premium: The best IT policies, templates, and tools, for today and tomorrow. Analog multimeters must be reset or zeroed out every time the range setting is altered and before testing the component. We use cookies to make wikiHow great. Ideally, if test leads touch (are shorted together), the display should show 0 Ω. Any 'component' has resistance. Multimeter probe tips are often sharpened to a needle-point. Understanding Bash: A guide for Linux administrators, Checklist: Managing and troubleshooting iOS devices, Comment and share: How to use a multimeter to test resistors. You can check the resistance of a resistor with an ohmmeter. Research source That implies a low resistance between them. 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. A thermistor is a resistor whose resistance changes according to the temperature it is exposed to.. This article was co-authored by Bess Ruff, MA. How to Test an Inductor with a Multimeter. If the resistor is in circuit, you will generally have to remove the resistors in the board so you are testing only the resistor value and not the other … Read on for another quiz question. Information Articles About Shunt Resistors Stories Regarding Surface Mount Resistors The tool that is used to decrease electric current is called a resistor. IMPORTANT: There's a good chance that you won't see exactly the resistance values I've listed (on your multimeter). 5 ways tech is helping get the COVID-19 vaccine from the manufacturer to the doctor's office, PS5: Why it's the must-have gaming console of the year, Chef cofounder on CentOS: It's time to open source everything, Lunchboxes, pencil cases and ski boots: The unlikely inspiration behind Raspberry Pi's case designs. Place one lead of the Ohmmeter on terminal 1 of the resistor. We all know that the resistance of an LDR varies according to the light falling on it. Testing a Resistor with an ohmmeter is the best, easiest and most effective way to tell whether a resistor is good or not. The two and a half million value resistor is good if the meter reads between 2,250,000 and … However, that’s not because switches and relay contacts can’t be measured for resistance. If resistance does not show any reading, what should I do? Any capacitors in a circuit being tested for resistance should be discharged before testing. A resistance test of a contactor shows a coil resistance of around 97 Ohms. Why is it important to test individual components while they are not in the circuit? The colors and the values they represent are as follows: black (0) brown (1) red (2) orange (3) yellow (4) green (5) blue (6) violet (7) grey (8) white (9). One of these answers is absolutely an indication that your starting range is inaccurate, but the others are not. There are many historical units no longer in use. If the needle swings to 20 kiloohms, that’s probably the resistance of the component you’re testing. If this circuit is open, showing infinity on the Ohmmeter, the blower resistor must be replaced. A silver stripe defines a +/-10% tolerance, and a gold stripe defines a +/- 5% tolerance. The colored stripes define the resistance in ohms and its tolerance. Not necessarily! Test again to verify the results! ", very solid foundation. Wait for the reading to stabilize and then you should have your result. If it is showing 1 or OL, turn the range up. Turn the resistor so that this band is to your right. Yup! Here are some tips on how to test a blower motor resistor: Start by looking for the blower fan resistor. Not exactly! Test for power at all the blower speeds by moving the blower speed switch through all positions. You can also attach alligator clips to the multimeter probes to keep the terminals of the resistor or component in place while testing. Right! If the resistor is in circuit, you will generally have to isolate the resistor so you are measuring only the resistor, not other components in the circuit. Once you get in the right range, try lowering the range one more time to see if you can get a more accurate reading. At bright light, the LDR resistance will be around 500Ohms and at darkness the resistance will be around 200K. Unplug the blower motor and test for power using the 12-volt test light in the same manner as explained in Step 1. 26.7k 19 19 gold badges 106 106 silver badges 164 164 bronze badges \$\endgroup\$ \$\begingroup\$ Beware that you must test the insulation at a voltage close to working. The middle of the range is usually 20 kiloohms. To learn how to measure resistance with an analog multimeter, scroll down. Measuring Resistance with a Digital Multimeter, {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/e\/e2\/Measure-Resistance-Step-1-Version-2.jpg\/v4-460px-Measure-Resistance-Step-1-Version-2.jpg","bigUrl":"\/images\/thumb\/e\/e2\/Measure-Resistance-Step-1-Version-2.jpg\/aid1358321-v4-728px-Measure-Resistance-Step-1-Version-2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"