LCD Digital Multimeter (220-0185) Operation Faxback Doc. # 16931 MAKING MEASUREMENTS DC/AC Voltage Measurements IMPORTANT: The maximum input limit for voltage measurement is 1000 V/DC and 750 V/AC (RMS). If you attempt to measure DC voltages above 1000 volts or AC volts above 750 volts RMS, the unit may be damaged. All the figures on the display will blink when more than the maximum rate (DC 1000 V/AC 750 V) is supplied: DISCONNECT PROBES IMMEDIATELY. 1. Set the function switch to DC V or AC V. 2. Set the range switch 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 position and reduce the setting as required to obtain a satisfactory reading. 3. Plug the red lead into the + jack and the black lead into the - COM jack. 4. Connect the probes to the circuit to be tested. In DCV, the minus sign will appear if voltage is negative. 5. Read the range by the position of the decimal point. NOTES: On 300 V and 300 mV ranges, the decimal point will appear in the same position (one place to the left), but if the 300 mV range is selected, "mV" will appear on the display. If the function switch is rapidly shifted from Kohm to DCV with the range switch set to the 300 mV position, the display might show the over-range indication because of the high input impedance. Short the test leads to remove this condition. When measuring DCV or ACV with no circuit under test, the display may show small changes in the lower ranges. This is normal. A high input impedance produces this "wandering" effect. As soon as a circuit is connected, normal accurate measurement is performed. HINTS: When you are using the meter to probe for a voltage in a high voltage circuit, we recommend that you do not try to position both of the probes at once. Instead, you should clamp one of the leads to the neutral or ground lead of the circuit (usually a bare, green or white lead, in AC wiring circuits) using our insulated Slip-On Alligator Clips (Cat. No. 270-354), and then probe for voltages with the other probe. This helps to prevent you from accidentally touching a "hot" wire, since you need only concentrate on one test probe. Never clamp on to a "hot" wire, usually red, black, or blue in AC wiring circuits), since if you did so and then touched the other probe connected to the meter, you could receive an electric shock. AC Voltage Riding on a DC Source Bias Measurement You can measure an AC voltage superimposed on a DC voltage source bias. Set the function switch to ACV. However, NEVER ATTEMPT TO MEASURE ANY CIRCUIT OVER 750V AC with respect to earth ground. Measuring 3-Phase AC Voltages This meter is designed primarily to measure household AC voltages. When measuring 3-phase circuits line-to-line, the value of the voltage will actually be higher than the rated line-to ground 3-phase voltage. It is important that you do not exceed the maximum PEAK AC rating of this meter, which is 750V AC. To determine the highest possible voltage on a 3-phase line, multiply the stated voltage by the square root of three (approximately 1.75). Severe damage as well as a dangerous shock hazard could result if the meter is connected to a circuit that exceeds the voltage rating of the meter. DC/AC Current Measurements To measure current, you must break the circuit and connect the leads to two circuit connection points. NEVER CONNECT THE LEADS ACROSS A VOLTAGE SOURCE; doing so will blow the fuse or damage the circuit under test. The maximum input limit for DC current/AC current measurement is 10A (with red lead plugged to 10A jack). 1. Set the function switch to DCmA or ACmA. 2. Set the range switch to the desired position. 3. For 300 mA max., plug the red lead into the + jack, and the black lead into the - COM jack. For 10A max., plug the red lead into the 10A jack, and the black lead into the - COM jack. 4. Remove power from the circuit under test and then break the circuit at the appropriate point. 5. Connect probes to the circuit in series. 6. Apply power and read current. 7. If the polarity of the current being measured is negative in DC measurement, the value displayed will be preceded by a minus (-) sign Input of more than the maximum rate (DC/AC 10A) will cause the display to blink on and off as a warning. NOTE: All current ranges except the 10A are fuse-protected. If inoperative, check the fuse. Resistance Measurements NOTE: The resistance measuring circuit compares the voltage which is gained through a known resistance (internal) with the voltage developed across the unknown resistance. Thus when checking "in- circuit" resistance, be sure the circuit under test has all power removed (are all capacitors fully discharged?). 1. Set the function switch to the kohm position. 2. Set the range switch to the desired position. 3. Plug the red test lead into the + jack and the black lead into the - COM jack. 4. Connect the probes across the circuit to be measured. 5. For resistances of approximately 1 megohm and above, the display may take a few seconds to stabilize. This is normal for high resistance readings. Use the measuring unit display to see the range you are in. "Ohm" or "Kohm" to distinguish between 300 ohm and 300 kohm, "Megohm" or "Kohm" for 30 Megohms vs. 30 kohms. NOTES: The unit has a circuit to protect the resistance ranges from over- voltage (500V AC 1 minute). To prevent accidentally exceeding the rating of the protection circuit and to ensure the correct measurement, never connect the probes to a source of voltage when the function switch is set to the kohm or diode check position. Some devices could be damaged by the current applied during resistance measurements. The table below lists the voltage and current available for each. Range A B C 300 ohm 3.0 V 180 mV 700 MicroA 3 k 1.3 V 310 mV 140 MicroA 30 k 1.3 V 400 mV 20 MicroA 300 k 1.3 V 460 mV 2 MicroA 3000 k 0.7 V 440 mV 0.4 MicroA 30 M 0.7 V 440 mV 0.04 MicroA * A is the open circuit voltage at the jacks in volts. * B is the voltage across a resistance equal to full scale value. * C is the current through a short circuit at the input jacks. All values are typical. When you short the test leads in the 300 ohm range, a small value (no more than 0.3 ohms) will be displayed. This is due to internal circuit and test leads resistance. You may need to take note of this value and deduct it from the measured value when you measure very small resistances. Continuity Function This tester has a built-in audible continuity function. 1. Set the power switch to the CONTINUITY function. 2. Set the function switch to kohn. The range is automatically set to 320 ohm. 3. Connect the red lead into the + jack and the black lead into the - COM jack. 4. Connect the probes to the circuit you want to check. 5. If the circuit resistance is 300 ohms or less, the buzzer will sound. NOTE: When the switch is in the CONTINUITY position, the buzzer will also sound when: 1. The function or range switch is changed. 2. Over-range takes place (except in kohn and diode check functions). Diode Check 1. Set the function switch to the diode check position. The range is automatically set to 3V. 2. Plug the red test lead into the + jack and the black lead into the - COM jack. 3. Remove power from the circuit under test. 4. Connect the probe to the semiconductor device you want to check and note the meter reading. 5. Reverse the probes and note the second reading. If the first reading shows some value and second is overrange, the device is good. If both are overrange, the device is open. If the reading are both very small or zero, the device is shorted. NOTE: The values indicated on the display during the diode check operation shows the actual forward voltage (max. 2V). If the value is around 0.400 the device is germanium type: if it is around 0.600 the device is silicon type. An LED will make the meter display a value of about 1.800. FUSE REPLACEMENT WARNING: TO AVOID ELECTRIC SHOCK, DISCONNECT THE TEST PROBES BEFORE REMOVING BATTERIES OR FUSE. REPLACE ONLY WITH SAME TYPE OF BATTERIES OR FUSE. THIS INSTRUMENT CONTAINS NO USER SERVICEABLE PARTS. SERVICE SHOULD BE PERFORMED ONLY BY QUALIFIED PERSONNEL. CAUTION: FOR CONTINUED PROTECTION AGAINST FIRE, REPLACE ONLY WITH 0.5A, 250V FUSES (Cat. No. 270-1241). 1. Be sure POWER is OFF and test leads are disconnected. 2. Open the battery/fuse compartment cover. 3. Pull the red ribbon in the fuse compartment; the fuse will pop out. NOTE: The fuse in the digital multimeter is a special size and type. One spare fuse comes supplied with the unit. 4. Insert a new fuse on the ribbon ring. Use only a fuse of the same type/rating (0.5A, 250V, 5X20 mm miniature fuse; Radio Shack Cat. No. 270-1241). 5. Install the new fuse with ribbon in the fuse compartment. 6. Close the battery/fuse compartment. WARNING: DO NOT OPERATE THE UNIT UNTIL THE BATTERY/FUSE COVER IS IN PLACE AND FULLY CLOSED.