Digital Multimeter (220-0168) Operation Faxback Doc. # 7953 with PC Interface MAKING MEASUREMENTS UNDERSTANDING PHANTOM READINGS In some DC and AC voltage ranges, when the probes are not connected to any circuit, the display might show a phantom reading. This is normal. The meter's high input sensitivity produces a wandering effect. When you connect the probes to a circuit, accurate readings appear. MEASURING HIGH-VOLTAGE CIRCUITS When you use the meter to check a high-voltage circuit, do not try to position both probes at once. Instead, clamp one probe to the neutral or ground lead of the circuit (usually a bare, green, or white wire in AC wiring circuits) using insulated Slip-On Alligator Clips (Cat. No. 270-354). Then probe for voltages with the other probe. This helps prevent you from accidentally touching a hot wire because you need to concentrate on only one test probe. Warning: Never clamp onto a hot wire, (usually red, black, or blue in AC wiring circuits.) If you clamp onto a hot wire and touch the other probe, you could receive a shock. AC/DC VOLTAGE MEASUREMENT WARNING: DO NOT TRY TO MEASURE A VOLTAGE GREATER THAN 1000 VOLTS DC OR 750 VOLTS AC. YOU MIGHT DAMAGE YOUR METER AND EXPOSE YOURSELF TO A SEVERE SHOCK HAZARD. Note: All the figures on the display blink when more than the maximum voltage (DC 1000/AC 750 VOLTS) is supplied. If this happens, DISCONNECT THE PROBES IMMEDIATELY. Follow these steps to measure AC/DC voltage. 1. Rotate the function selector to the desired position. Select the range as required for the voltage level to be measured. If you do not know the voltage level, start with the range switch set to the highest voltage position and reduce the setting as needed to get a reading. 2. Press DC/AC to toggle between DC and AC voltage. AC appears for AC measurements. 3. Plug the black probe into the meter's COM terminal and the red probe into the V ohms terminal. 4. Connect the probes to the AC/DC voltage source you want to measure. Notes: If polarity is negative, - appears on the left of display. For the most accurate measurement, select the lowest possible voltage range without getting an overload reading. Measuring an AC Voltage on a DC Bias To measure an AC voltage superimposed on a DC voltage source bias, follow the steps for measuring AC voltage. Caution: Never try to measure an AC voltage that is riding on a DC voltage level where the peak AC Voltage exceeds 1000V with respect to earth ground. MEASURING 3-PHASE AC VOLTAGES We designed this meter to measure household AC voltage. It is not intended for commercial or industrial use. If you want to measure 3-phase, line-to line voltages, please note the following. Warning: Because of the dangers inherent in measuring three-phase circuits, we strongly recommend that you do not use the meter for such applications. If you choose to make the measurements, use extreme care. The actual voltage can be greater than the circuit's rated voltage (line-to-ground). To determine the line-to-line voltage, multiply the rated line-to-ground voltage by 1.732. For example, if the rated line-to-ground voltage is 462 volts, the line-to-line voltage is: 462 Volts X 1.732=800 Volts This voltage exceeds the meter's rating and you should not connect the meter to this circuit. See "Measuring High-Voltage Circuits." MEASURING AC/DC CURRENT WARNINGS: DO NOT APPLY VOLTAGE DIRECTLY ACROSS TERMINALS. YOU MUST CONNECT THE METER IN SERIES WITH THE CIRCUIT. THE 20A TERMINAL IS FUSED. A SEVERE FIRE HAZARD AND SHORT CIRCUIT DANGER EXISTS IF YOU APPLY A VOLTAGE WITH HIGH-CURRENT CAPABILITY TO THIS TERMINAL. THE METER CAN BE DESTROYED UNDER SUCH CONDITIONS. To measure current, break the circuit and connect the probes to two circuit connection points. Never connect the probes across a voltage source in parallel. Doing so can blow the fuse or damage the circuit under test. Note: The maximum input current is 200 mA or 20 A depending on the terminal used. In these ranges excessive current blows the fuses, which you must replace. 1. Rotate the function selector to the desired A range. If you do not know the current level, set it to the highest position and reduce the setting as needed to get a reading. 2. Press DC/AC to toggle between DC and AC amps. 3. Plug the black probe into your meter's COM terminal and the red probe into your meter's mA or 20A terminal. 4. Remove power from the circuit under test and then break the circuit at the appropriate point. 5. Connect the probes in series with the circuit. 6. Apply power and read the current. Your meter displays the current value. Note: If you set the meter for DC current, - appears or disappears. This indicates the polarity of the measured current. MEASURING CAPACITANCE Follow these steps to measure normal capacitance. 1. Before testing, discharge each capacitor by shorting its leads together. Use caution when handling some capacitors, as they can be charged with considerable electricity. Caution: If you attempt to measure the capacitance of a charged capacitor, you might damage your meter. 2. Rotate the function selector to the desired CAP range (LO for low-value capacitors and HI for High-value capacitors). If you do not know the approximate capacitance value, set the range to HI and reduce to LO to get a valid reading. 3. Insert the discharged capacitor into the CAP connectors. Your meter displays the capacitance values. Notes: For polarized capacitors, be sure to insert the negative lead in the -clip. In this mode's HI range, the auto power off function does not work. MEASURING RESISTANCE WARNINGS: NEVER CONNECT THE TEST PROBES TO A SOURCE OF VOLTAGE WHEN YOU HAVE SELECTED THE OHMS FUNCTION AND PLUGGED THE PROBES INTO THE V/OHMS TERMINAL. BE SURE THAT THE CIRCUIT UNDER TEST HAS ALL POWER REMOVED AND THAT ANY ASSOCIATED CAPACITORS ARE FULLY DISCHARGED BEFORE YOU MAKE A RESISTANCE MEASUREMENT. The resistance measuring circuit compares the voltage gained through a known resistance (internal) with the voltage developed across the unknown resistance. So, when you check in-circuit resistance, be sure the circuit under test has all power removed (all capacitors are fully discharged). 1. Plug the black probe into your meter's COM terminal and the red probe into your meter's V/OHM terminal. 2. Rotate the function selector to the desired OHM range. 3. Connect the probes to the device you want to measure. Notes: If the measured resistance value exceeds the maximum value of the range selected, OL appears and the bargraph flashes. This indicates an overload. Select a higher range. In this mode, the beeper does not sound. When you short the test probes in the 200 OHM range, your meter displays a small value (no more than 0.3 ohms). This value is due to your meter's and test lead's internal resistance. Make a note of this value and subtract it from small resistance measurements for better accuracy. For resistance of about 1 Megohm and above, the display might take a few seconds to stabilize. This is normal for high-resistance readings. CHECKING DIODES This function lets you check diodes and other semiconductors for opens and shorts. It also lets you determine the forward voltage for diodes. You can use this function when you need to match diodes. 1. Plug the black probe into your meter's COM terminal and the red probe into your meter's V/OHMS terminal. 2. Rotate the function selector to the diode position. 3. Connect the probes to the diode you want to check and note the meter reading. If the display shows a value, for example 0.2 for a geranium diode or 0.5 for a silicon diode, reverse the diode. If the meter indicates an overrange, the diode is good. The displayed number is the diode's actual forward voltage (up to 2.0 volts). If the display indicates an overrange condition, reverse the polarity of the connection. If the display shows a value, the device is good. The displayed value is the component's actual forward voltage (up to 2.0 volts). If the display still indicates an overrange condition, the device is open. If the display shows a value both before and after you reverse the polarity, the device is shorted. When you connect the diode to the meter and the meter displays the device's forward voltage, the red test probe or socket is connected to the diode's anode, and the black probe or socket is connected to the diode's cathode. This meter supplies enough forward voltage to light most LEDs. However, if the LED's forward voltage is greater than 2.0 volts, the meter incorrectly indicates that the device is open. CHECKING CONTINUITY Follow these steps to check a circuit's continuity. 1. Rotate the function selector to MUSIC SYMBOL. 2. Plug the black probe into your meter's COM terminal and the red probe into your meter's V/OHM terminal. 3. Remove power from the circuit. Warning: Never perform a continuity measurement on a circuit that has power connected. 4. Connect the probes to the circuit. Note: The buzzer sounds if the measured resistance is below 40 ohms. CHECKING TRANSISTORS Follow these steps to determine a transistor's base gain. 1. Rotate the function selector to the hFE position. 2. Insert the transistor you want to measure into the appropriate transistor socket. Your meter displays the transistor's hFE value. Notes: Insert the base, collector, and emitter pins in the correct sockets, as marked. Do not take the hFE reading as an absolute measurement, but rather as an indication that the transistor is operating. The true gain of a transistor depends on its operating current. This meter applies 500 to 1000 microA to the emitter and collector and measures the base current to calculate the base gain. Even though the meter turns off the test probes during the hFE measurement, a voltage connection might affect the hFE reading. Do not connect the test probes to a voltage source during this measurement. You cannot measure the hFE of a transistor that is connected in a circuit. You cannot measure the hFE of an FET or other non-bipolar transistor. Some power Darlington transistors contain an internal base-to- emitter resistor. Because the meter uses two current readings to calculate hFE, any internal transistor resistance causes undependable readings. High-voltage junctions in power transistors prevent correct readings. Also, the larger leads of the power transistor can damage the test socket. Do not try to determine hFE for power transistors with this meter. hFE is affected by temperature. Try not to warm the transistor with your hand when you install the device in the socket. If the hFE reading is not stable when you first measure it, let the transistor's temperature stabilize. Warning: The transistor socket is not protected against overload. You can damage the meter and void your warranty if you build and use external leads for the transistor socket. MEASURING FREQUENCY WARNING: IF YOU TRY TO MEASURE THE FREQUENCY OF A SIGNAL THAT EXCEEDS 250 VOLTS AC RMS, YOU MIGHT DAMAGE YOUR METER AND EXPOSE YOURSELF TO A SEVERE SHOCK HAZARD. Follow these steps to measure the frequency of a signal. 1. Rotate the function selector to FREQ. 2. Plug the black probe into your meter's COM terminal and the red probe into your meter's V/OHM terminal. 3. Connect the probe to the frequency source. Notes: Input limit voltage: AC 250 V max. Input sensitivity: 1 Hz up to 1 MHz - 150 mV rms. 1 MHz up to 20 MHz - 300mV rms. Warning: When you connect the test probes to an AC outlet, do not turn the function selector switch to another range. It could damage the meter's internal components or injure you. LOGIC TEST The logic function lets you easily check digital circuits to determine the logic state of different parts of the circuit. Rather than display an absolute voltage, this function displays HI, LO, or--- to indicate logic high, logic low, or undetermined, respectively. Follow these steps to perform a logic test. 1. Rotate the function selector to the HIGH/LOW logic range. 2. Plug the black probe into your meter's COM terminal and the red probe into your meter's V/OHM terminal. 3. Connect the black probe to the ground point (GND of the test circuit and the red probe to the supplying voltage point (V+). While keeping the test probes firmly connected to each point, press SET/RESET. 4. While keeping a connection between the black probe and the circuit's GND point, move the red probe to the other desired points. The meter immediately displays one of the three indications. If the measured value exceeds 70% of the stored (V +) value, Hi (HIGH) appears. If the measured value is between 30% and 70% of the stored (V +) value, --- appears. Notes: In this mode, the Data-Hold and Max/Min-Hold functions do not work (See "Using the Advanced Functions"). The logic level is limited to a voltage range of 0.5 V to 19.9V. (br/all-01/17/95)