User's Guide Digital Multimeter Extech 420
Introduction Congratulations on your purchase of the Extech 420 (part number EX420) Autoranging Multimeter. This meter measures AC/DC Voltage, AC/DC Current, Resistance, Capacitance, Frequency, Duty Cycle, Diode Test, and Continuity plus Thermocouple Temperature. Proper use and care of this meter will provide many years of reliable service. Safety International Safety Symbols This symbol, adjacent to another symbol or terminal, indicates the user must refer to the manual for further information.
CAUTIONS • Improper use of this meter can cause damage, shock, injury or death. Read and understand this user manual before operating the meter. • Always remove the test leads before replacing the battery or fuses. • Inspect the condition of the test leads and the meter itself for any damage before operating the meter. Repair or replace any damage before use. • Use great care when making measurements if the voltages are greater than 25VAC rms or 35VDC. These voltages are considered a shock hazard.
OVERVOLTAGE CATEGORY III This meter meets the IEC 610-1-2001 standard for OVERVOLTAGE CATEGORY III. Cat III meters are protected against overvoltage transients in fixed installation at the distribution level. Examples include switches in the fixed installation and some equipment for industrial use with permanent connection to the fixed installation. SAFETY INSTRUCTIONS This meter has been designed for safe use, but must be operated with caution.
Controls and Jacks 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 4000 count LCD display HOLD SELECT button Function switch mA, uA and A input jacks COM input jack Positive input jack RANGE hold button RELATIVE button Backlight button Protective holster Note: Tilt stand and battery compartment are on rear of unit.
Operating Instructions WARNING: Risk of electrocution. High-voltage circuits, both AC and DC, are very dangerous and should be measured with great care. 1. ALWAYS turn the function switch to the OFF position when the meter is not in use. 2. If “OL” appears in the display during a measurement, the value exceeds the range you have selected. Change to a higher range. NOTE: On some low AC and DC voltage ranges, with the test leads not connected to a device, the display may show a random, changing reading.
AC VOLTAGE MEASUREMENTS WARNING: Risk of Electrocution. The probe tips may not be long enough to contact the live parts inside some 240V outlets for appliances because the contacts are recessed deep in the outlets. As a result, the reading may show 0 volts when the outlet actually has voltage on it. Make sure the probe tips are touching the metal contacts inside the outlet before assuming that no voltage is present. CAUTION: Do not measure AC voltages if a motor on the circuit is being switched ON or OFF.
AC CURRENT MEASUREMENTS CAUTION: Do not make current measurements on the 20A scale for longer than 30 seconds. Exceeding 30 seconds may cause damage to the meter and/or the test leads. 1. Insert the black test lead banana plug into the negative COM jack. 2. For current measurements up to 4000µA AC, set the function switch to the yellow µA position and insert the red test lead banana plug into the µA/mA jack 3.
CONTINUITY CHECK WARNING: To avoid electric shock, never measure continuity on circuits or wires that have voltage on them. 1. Set the function switch to the green position. 2. Insert the black lead banana plug into the negative COM jack. Insert the red test lead banana plug into the positive Ω jack. 3. Press the SELECT button to indicate on the display. 4. Touch the test probe tips to the circuit or wire you wish to check. 5. If the resistance is less than approximately 150Ω, the audible signal will sound.
CAPACITANCE MEASUREMENTS WARNING: To avoid electric shock, disconnect power to the unit under test and discharge all capacitors before taking any capacitance measurements. Remove the batteries and unplug the line cords. 1. Set the rotary function switch to the green position. 2. Insert the black test lead banana plug into the negative COM jack. Insert the red test lead banana plug into the positive jack. 3. Touch the test leads to the capacitor to be tested. 4.
CONTACT TEMPERATURE MEASUREMENTS 1. Set the function switch to the black Type K ºC or ºF position. 2. Insert the Temperature Probe into the input jacks, making sure to observe the correct polarity. 3. Touch the Temperature Probe head to the part whose temperature you wish to measure. Keep the probe touching the part under test until the reading stabilizes (about 30 seconds). 4. Read the temperature in the display. Note: The temperature probe is fitted with a type K mini connector.
AUTORANGING/MANUAL RANGE SELECTION When the meter is first turned on, it automatically goes into AutoRanging. This automatically selects the best range for the measurements being made and is generally the best mode for most measurements. For measurement situations requiring that a range be manually selected, perform the following: 1. 2. Press the RANGE key. The AUTO display indicator will turn off. Press the RANGE key to step through the available ranges until you select the range you want. 3.
Specifications Function DC Voltage Range 400mV Resolution 0.1mV 4V 40V 400V 1000V 0.001V 0.01V 0.1V 1V 400mV 0.1mV 4V 40V 400V 750V 0.001V 0.01V 0.1V 1V Accuracy ±(0.3% reading + 2 digits) ±(0.5% reading + 2 digits) ±(0.8% reading + 3 digits) 50 to 400Hz 400Hz to 1kHz AC Voltage DC Current ±(1.5% reading + 15 digits) ±(2.5% reading + 15digits) ±(1.5% reading + 6 digits) ±(2.5% reading + 8 digits) ±(1.8% reading + 6 digits) ±(3% reading + 8 digits) 400μA 0.
Function Frequency Duty Cycle Range Resolution Accuracy 5.000Hz 0.001Hz ±(1.5% reading + 5 digits) 50.00Hz 0.01Hz 500.0Hz 0.1Hz 5.000kHz 0.001kHz ±(1.2% reading + 2 digits) 50.00kHz 0.01kHz 500.0kHz 0.1kHz 5.000MHz 0.001MHz ±(1.5% reading + 4 digits) 10.00MHz 0.01MHz Sensitivity: 0.8V rms min. @ 20% to 80% duty cycle and <100kHz; 5Vrms min @ 20% to 80% duty cycle and > 100kHz. 0.1 to 99.9% 0.1% ±(1.
Maintenance WARNING: To avoid electrical shock, disconnect the meter from any circuit, remove the test leads from the input terminals, and turn OFF the meter before opening the case. Do not operate the meter with an open case. This MultiMeter is designed to provide years of dependable service, if the following care instructions are performed: 1. KEEP THE METER DRY. If it gets wet, wipe it off. 2. USE AND STORE THE METER IN NORMAL TEMPERATURES.
REPLACING THE FUSES WARNING: To avoid electrical shock, disconnect the meter from any circuit, remove the test leads from the input terminals, and turn OFF the meter before opening the case. Do not operate the meter with an open case. 1. Disconnect the test leads from the meter. 2. Remove the protective rubber holster. 3. Remove the battery cover (two “B” screws) and the battery. 4. Remove the four “A” screws securing the rear cover. 5.
