Using Test Equipment
Using Test Equipment
Using Test Equipment
G-21
INTRODUCTION
The volt-ohmmeter, usually referred to as a VOM, or Multimeter, combines two individual instruments into one. These instruments are the: Ohmmeter for measuring resistance (in ohms - ). Voltmeter for measuring voltage (AC and DC). Technicians prefer the convenience of this single meter that combines both measuring functions. Some multimeters offer other functions, such as AC ampere, DC millivolt, and temperature measurements.
Display
AC-DC Selector
Display
Probe Jacks
Temperature Adapter
Test Leads
7. Look straight at the meter pointer and scale. If you view them at an angle, you can get an inaccurate reading. Some meters have a mirrored scale to help prevent reading errors. With this type of scale, you know that you are viewing straight if the pointer hides its reflection in the mirror (see Figure 3).
Pointer Reflection
No Pointer Reflection
Mirror
Figure 3
8. Select the appropriate voltage or resistance range so that the readings are in the center portion of the scale. This will give a more accurate reading (see Figure 4). Midrange Viewing
Figure 4
RESISTANCE
MEASURING RESISTANCE ()
When a resistance measurement is made, the test probes connect the meter in series with the component, or load. To prevent damage to the meter during a resistance measurement, the circuit or component is always disconnected from the power source. A very small current is needed to obtain a resistance measurement, and is provided by a battery inside the VOM. Note that the resistance, or ohms scale () of the meter, is the reverse of the volts scales (see Figure 5). That is, the zero on each scale is at the opposite ends of the meter.
Figure 5
When the maximum amount of current is flowing through the circuit, the pointer will rotate all the way to the zero end of the ohms scale. When very little current is flowing, the pointer will remain at, or near, the infinity (), or maximum resistance, end of the ohms scale. The Range switch has various resistance values built into the meter, which allows for the proper measurement of resistance. Before making a resistance reading, any changes in the battery condition must be compensated for to assure accuracy. In order to do this: 1. Touch the test lead probe tips together to obtain the maximum current flow from the battery. 2. Zero the resistance scale pointer with the Ohms Zero Adjustment knob. 3. Zero the meter each time the range switch is changed. 7
Figure 6
Unlike voltage scales, the scale used for resistance measurements is not divided into equally-spaced increments. As resistance becomes higher, the numbers on the scale are grouped closer together, making an accurate reading difficult (see Figure 7).
Difficult Viewing
Figure 7 When making resistance measurements, it is important to try to get a lower, or midscale reading, whenever possible (see Figure 8).
750 On R x 1 Scale
MEASURING CONTINUITY
The ohmmeter can also be used to check continuity in a circuit. Continuity is a continuous, or closed circuit. An open circuit means that the continuous circuit has been broken at some point. In this case, the meter would indicate infinite resistance. Figure 9 shows an open and a closed circuit.
Open
Figure 9
10
R x 10K
1.
R x 1K
2.
Rx1
3.
4.
R x 100
11
R x 10K
1.
5000
R x 1K
2.
2500
Rx1
3.
.6
4.
R x 100 820
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VOLTAGE
THE RANGE SWITCH
The Range switch has various settings for DC volts and for AC volts. Both types of voltage have ranges with six settings: 2.5, 10, 25, 100, 250, and 500 volts (see Figure 10). The AC - DC Selector switch selects the type of voltage being measured (DC, +DC, AC).
Figure 10
Figure 11A
13
Figure 11B
c) The 0 - 250 scale is used with the 2.5, 25, or 250 volt ranges.
Figure 11C
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Figure 12
15
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MEASURING VOLTAGE
Example 1 To measure a 9-volt battery, touch the meter probes to the battery terminals. The needle moves across the voltage scale to the point, shown in Figure 13.
Figure 13 Since the 10-volt range is selected, the reading will be taken on the 0 - 10 scale. Each increment on the scale represents .2 volts. Read the pointer location on the scale between the 8 and the 10. It should indicate approximately 9 volts. Example 2 To measure a 20-volt battery: a) Set the Range switch to the 25V position. b) Touch the meter probes to the battery terminals. c) Read the pointer on the 0 - 250 scale. d) The pointer should indicate approximately 200 on the scale. Since the range switch is set for 25V, divide the reading by 10 (200 10 = 20). Example 3 To measure a 280-volt circuit: a) Set the Range switch to the 500V position. b) Touch the meter probes to the circuit terminals. c) Read the pointer on the 0 - 50 scale. d) The pointer should indicate approximately 28 on the scale. Since the range switch is set for 500V, multiply the reading by 10 (28 x 10 = 280). 17
25V
1.
10V
2.
100V
3.
500V
4.
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NOTES
19
25V
1.
19V
10V
2.
2.8V
100V
3.
45V
500V
4.
315V
20
Figure 14
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To measure with a load: 1. Plug the appliance into the receptacle and turn on the appliance (see Figure 15). 2. Insert the meter probe tips into the empty receptacle. 3. Read the meter. Under load conditions, the reading may be slightly less than under no load conditions. IMPORTANT: Appliances with heavy drive motors, such as washers and dishwashers, should also be tested at the moment of start. If the voltage drops more than ten percent, (less than 108 volts), when the motor is started, it means that there is a problem with the electrical supply (the electricity coming into the receptacle). Mark this on the service invoice. State that there is a problem with the circuit, and that the customer has been informed.
Figure 15
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Figure 16 23
To test for polarity: 1. Test that there is line voltage between the long and short slots (120 volts) (see Figure 17A). 2. Test that there is line voltage between the short slot and the round hole (ground receptacle) (see Figure 17B), or the center screw (120 volts) (see Figure 17C). 3. Test that there is NO VOLTAGE between the long slot and the ground receptacle (see Figure 17D), or center screw (see Figure 17E).
Figure 17 CAUTION: IF THE OUTLET IS IMPROPERLY WIRED, THE THREE TESTS, SHOWN ABOVE, WILL FAIL. A LICENSED ELECTRICIAN MUST CORRECT THE PROBLEM. REMEMBER: The short slot is HOT, the long slot is NOT.
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Figure 18
25
5. Touch the meter probe tips to the indicated outlet openings (see Figure 19). The meter should measure approximately 120 volts AC.
Figure 19
6. Touch the meter probe tips to the indicated outlet openings (see Figure 20). The meter should measure approximately 120 volts AC.
Figure 20
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Figure 21
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5. Touch the meter probe tips to the indicated outlet openings (see Figure 22). The meter should measure approximately 120 volts AC.
Figure 22 6. Touch the meter probe tips to the indicated outlet openings (see Figure 23). The meter should measure approximately 240 volts AC.
Figure 23
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7. Touch the meter probe tips to the indicated outlet openings (see Figure 24). The meter should measure 0 volts.
Figure 24
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MANOMETER
When it becomes necessary to measure gas pressure, there are two instruments available that you can use: a manometer, like the one shown on this page, and a magnehelic gauge (shown on page 32). A manometer is basically a U-shaped tube with a scale, marked in inches of water column. To prepare and use the manometer, use the following steps:
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1. Check the appliance model/serial plate and note the gas pressure rating. 2. Turn off the gas pressure to the range. 3. Prepare the manometer by filling the Ushaped tube with water so that both sides of the tube fill to the zero point (see Figure 25). NOTE: Use a little food coloring in the water to help make reading the meter easier.
Figure 25 4. Connect the tubing that is supplied with the manometer over one end of the manometer. 5. Remove a burner from the appliance and place the free end of the tubing over the burner orifice. 6. Turn on the gas supply to the range. 7. Turn on the gas valve being tested, and light at least one other burner to serve as a load. 8. Observe the movement of the water in the manometer. The gas pressure is read by adding the water movement in both legs of the tube, as shown in Figure 26. It should measure within the pressure rating stated on the rating plate.
Figure 26
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MAGNEHELIC GAUGE
The Magnehelic Gauge measures gas pressure. This type of gauge is easier and faster to use than a manometer. To use the gauge: 1. Check the appliance model/serial plate and note the gas pressure rating. 2. Turn off the gas pressure to the range. 3. Remove a burner from the appliance and place the free end of the tubing over the burner orifice. 4. Turn on the gas supply to the range. 5. Read the gas pressure directly from the scale of the gauge. It should measure within the pressure rating stated on the rating plate. Some gauges have numerous scales on the dial face. Read the water column pressure scale when taking the measurement. The Model G24507 Magnehelic Gauge is available from: Marsh Bellafram, Inc. 1-800-727-5646
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AMP CLAMP
The Fluke Model 30 Amp Clamp measures AC and DC current and voltage. To use the meter, simply clamp it around the circuit under test, and read the display for the appropriate measurement.
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A Thermocouple Temperature Tester is helpful whenever it is necessary to measure hot surface temperatures, or when calibrating gas or electric ovens. The Tester is easy to use, and provides accurate temperature measurements from 20F to 1350F. It is specially useful for measuring temperature inside self-cleaning ranges, because of its high temperature range. IMPORTANT: Do not zero the meter. It should always indicate the ambient (surrounding) temperature. To use the Thermocouple Temperature Tester, perform the following steps: 1. Place the end of the thermocouple lead inside the area to be tested. 2. For greater accuracy, place the face of the meter in a horizontal position.
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OPERATIONAL NOTES: 1. To avoid inaccurate readings, do not shorten the thermocouple lead, or severely bend it. 2. Do not place the instrument on top of the range during testing. The heat will make it difficult for the internal ambient temperature compensator to function properly. 3. With both the meter movement and the lead stabilized at the same ambient temperature, use the adjustment screw on the meter face to set the meter at the ambient temperature. The ambient temperature can be checked with an accurate glass thermometer. 4. If the instrument is suspected to be defective, check the lead and meter. Replace the lead first. If the problem still exists, the meter movement is faulty. The Model 14855 Thermocouple Temperature Tester is manufactured by: Robinair Division Sealed Power Corporation Robinair Way Montpelier, OH 43543
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On every microwave oven service call, a check for microwave energy emission must be performed. A properly operating door and seal assembly will normally register small emissions, but they must be no greater than 4 mw/cm2. When checking for R.F. leakage, use an approved R.F. measuring device to assure less than 4mw/cm2 emission at 5 cm distance with a maximum scan rate of 2.5 cm/second, in compliance with U.S. Government Department of Health, Education and Welfare 21CFR1030, Performance Standard for Microwave Ovens. IMPORTANT: The meter must not be used without the spacer cone in place. 1. Before each use, both the battery and the probe should be tested. To test the battery: a) Turn the selector knob to the Battery Test position. The meter should read above the green marker line on the meter. If this reading is below the green line, replace the battery.
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To test the probe: a) Turn the selector knob to Probe Test. The meter should read between the green lines. If it does not, the probe is damaged and should not be used. A defective probe cannot be replaced in the field and should be returned to the factory for repair. 2. To operate the Microwave Survey Meter: a) Turn the selection knob to the desired meter range. b) Allow two (2) minutes for the instrument to stabilize. NOTE: If the instrument has been stored in a very warm or cold area, it should be allowed to stabilize at room temperature with the selector switch ON until no zero drift is observed. c) Use the Zero Adjust knob and adjust the meter pointer to true zero. The probe must be shielded or removed from the vicinity of any R.F. field. d) Keep the probe handle perpendicular, place the tip of the cone against the surface to be measured, and the leakage level will be accurately registered on the meter. The spacer cone automatically gauges the detecting probe 5 cm from the test point. Always use the probe handle. DO NOT PLACE YOUR HAND NEAR THE CONE END OF THE PROBE. e) The Fast position of the meter may be used to locate the point of the highest leakage. Compliance readings should be taken with the switch in the Slow position. f) Zero the meter after each measurement. If there is a shift in the meter zero, the measurement will not be accurate. g) The selection knob should be turned to OFF when the meter is not in use. The Model Hl1501 Microwave Survey Meter is manufactured by: Holiday Industries, Inc. 14825 Martin Drive Eden Prarie, MN 55344 Phone: 612-934-4920 FAX: 612-934-3604 37
A tap tool (part #4372141) is required to perform a gas pressure check on gas ranges with sealed burners. The tap tool is a small extension that is used to lengthen the burner tube up to the cooktop area, so that a hose can be connected from a gas pressure measuring device. To connect the tap tool: 1. Remove the cooktop burner orifice from the burner to be tested. 2. Insert the tap tool in place of the burner orifice. 3. Perform the gas pressure test. 4. Remove the tap tool from the burner and reinstall the gas orifice.
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CIRCUIT TESTER
To assure proper operation of any appliance, the correct polarity and grounding of its electrical outlet is necessary. One of the first checks on appliances should be to verify that the wall outlet is wired correctly. A circuit tester can easily and quickly verify that an appliance is connected to a properly wired (120 VAC) wall outlet. A series of lights within the tester will perform the following tests: Test Function Open ground Open Neutral Open Hot Hot/Ground Reversed Hot/Neutral Reversed Correct LED Reading 000 000 000 000 000 000
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To use the Bacharach Model PCA-12 Carbon Monoxide Detector: 1. Follow the instructions provided with the test equipment to prepare the instrument. The unit will need a minute or so to warm up. 2. Let the oven operate for 7 minutes before taking measurements. Do not position the meter near the oven during this period. 3. Insert the tester probe into the oven vent. 4. Press the RUN keypad. 5. Wait for the CO Air Free reading to stabilize. 6. Record the test results. The Carbon Monoxide Detector is available by contacting the Consumer Assistance Center Safety Team at: 1-800-541-5746.
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POCKET THERMOMETER
DIGITAL
ANALOG
The pocket thermometer is a handy tool for measuring temperature. For example, it can measure freezer or refrigerator compartments, heated water from microwave ovens, and exhaust temperatures from dryer vents.
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The ACR Jr. Data Logger measures and stores changes in temperature. The Logger is used with a computer to store and retrieve the data. Simply place the ACR Jr. Data Logger wherever you would like to record temperature changes. The logger will automatically read and store data every 2 minutes. When you wish to retrieve the stored data, run the ACR Jr. Graph software on your computer.
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ROBINAIRE WATTMETER
The Robinaire Wattmeter, Model 14865, measures voltage, (120 and 240), amperage (up to 99.9 amps), and wattage (power consumption).
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The Compressor Start Tester is used to check the compressor for open grounds and open windings.
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The Electronic Leak Detector detects the presence of any refrigerant escaping from the sealed system.
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The Machine Level is used to level appliances after they are installed in their mounting locations. The Inspection Mirror is used to inspect around a brazed joint and should be able to fit in small spaces.
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NOTES
47
NOTES
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CORPORATION