This tutorial describes the basic functions of the Hewlett-Packard HP34401A digital multimeter (DMM).
With the increasing use of digital techniques in implementing
state-of-the-art measurement instruments, a great many features are added to the instrument that would be cost prohibitive in analog instruments. However, this tutorial will address itself only to the use of the DMM in measuring the basic electrical quantities of voltage, current, and resistance.
In addition to providing the common multimeter capability to measure voltage, current, and resistance, the HP34401A is also capable of measuring the frequency of periodic waveforms.
The HP34401A features autoranging, a 6-1/2 digit readout, provision for data storage and display, 2 and 4 wire techniques for resistance measurements, and a General Purpose Interface Board (GPIB) port for remote measurements.
Additional built-in features are available by menu selections. Among these features are the ability to configure the system for taking remote measurements, to store and display defined max-min values, to set high and low limits for go/no-go testing, to select triggering options, and to control the display. However, we will deal here only with the use of the instrument for the fundamental measurements of voltage, current, and resistance.
Each workstation is provided with a users manual for the student to use to become familiar with the full capability of the instrument.
Figure 1 shows the front panel controls used in selecting the quantity to be measured and the measurement range. Note the shaded areas outlined in the figure. These areas contain the Math and Menu switches which, as we pointed out, will not be discussed here. We are primarily interested in the controls for measuring the basic electrical quantities of voltage, current, frequency, and resistance. You will also note that two terminals used in making 4-wire resistance measurements are also shaded since 2-wire measurements are most commonly made. (The 4-wire method is used to compensate for lead resistance of the instrument when measuring extremely small resistances.)
Front panel selction switches are annotated in blue and black print.
In order to select a function annotated in blue, it is necessary to first depress the blue SHIFT key.
The RANGE/DIGITS section allows you to select auto-ranging or
manual ranging. In general the auto-range functions is most convenient
The switches under the FUNCTION section shown in Figure 1 are used to select the electrical quantity to be measured.
The functions annnotated in blue permit selection of the following measurements:
Diode check (when forward biased, diode voltage drop will be
displayed rather than resistance)
The functions annotated in black allows selection of the following measurements:
Continuity (beeper sounds if circuit continuity exists)
In the center lower portion of the front panel are three keys under the heading of RANGE/DIGITS . One key selects manual or automatic ranging while the other two keys are used to select the nbumber of significant digits to be displayed (4, 5, or 6 digits) and range. The digit numbers are annotated in blue and the shift key must first be depressed to select the number of digits desired. The number of digits can be selected in either manual or auto range modes.
The range keys are direction arrows which can only be used in the manual ranging mode. If in auto range, the meter will revert to the manual mode if the ranging keys are depressed.
Referring to Figure 1, the terminals used for the various measurement functions are shown at the extreme right side of the front panel. The terminals shown shaded are used only when making 4-wire resistance measurements. The center (LO) and upper (HI) upper terminals are used for voltage and resistance measurements; the center and lower (I) terminals for current measurements.
Voltage ranges : 100mV, 1 V, 10 V, 100 V, 1000 V (readings in
Current ranges : 10 mA, 100 mA, 1 A, 3 A (readings in true rms)
Frequency range : 3 Hz to 300 Hz (AC voltage/current readings)
Resistance ranges : 100 w, 1K, 10K, 100K, 1M, 100M
Frequency measurement range : 1.0 MHz