LAB INSTRUMENT REFERENCE EEC180A Purpose: This document provides an introduction to the lab instruments found in the EEC180A lab. These instruments include the HP 54600B oscilloscope, the HP 6205B dual power supply, the HP 6237B triple output power supply, and the HP 3312A function generator. The goal of this reference tutorial is to introduce the basic function and operating procedures for these instruments to students with little lab experience. For more detailed operating instructions, the manufacturer’s operating manuals should be consulted. I. The HP 54600B Oscilloscope Figure 1. Measuring a DC voltage with the HP 54600B oscilloscope The 54600B oscilloscope has many different features and functions. We will only introduce a few of the most basic uses of this oscilloscope. The 54600B oscilloscope has two input channels which can be used for measuring signals. In Figure 1, a 10X probe is used to connect a DC voltage to channel 1. In order for the voltage scale, which is measured along the vertical axis, to be accurate, you must set the probe type. To set the Mode (RUN) Ch. 1 input Ch. 2 input Ch. 1 control Softkey to set Ch. 1 Probe type Trigger controls Trigger Mode (Auto) Mode Controlsprobe type for channel 1, press the “1” button, which is just below the Volts/div knob for channel 1. Next, check that the correct probe type is highlighted under the Probe setting on the screen. If the probe type is not set correctly, use the soft-key just below the Probe heading to toggle the selection to the correct choice. Figure 1 shows that the Probe type has been correctly set to 10. Measuring a DC signal Figure 1 shows the measurement of a +5V DC signal. Notice that the ground reference for channel 1 is set to center-line of the grid. (The channel 1 ground reference level can be adjusted using the Position knob just above the channel 1 input BNC jack.) In the upper-left hand corner of the display, you can see that the scope is set to 2V/div on channel 1. Since the signal trace is 2.5 divisions above the center-line, the DC voltage is (2.5 div)*(2V/div) = 5.0V. Notice in the upper-right corner that the Trigger MODE is set to Auto and the scope is in RUN mode. To measure a DC signal, the Trigger MODE must be set to Auto or Auto Lvl. To set the Trigger MODE, press the MODE button and then press the soft-key under the desired selection. Figure 2. Measuring a square wave with the HP 54600B oscilloscope Measuring a periodic signal Figure 2 shows the measurement of the scope’s 0-5V ‘calibration’ signal. The Time/Div knob is used to adjust the scale of the time axis, which is the horizontal axis on the Calibration signal 0-5V, ~1.2 kHz Time scale 200 us/div Time scale control Voltage scale 2V/div Ch. 1 voltage scale control Ch. 1 gnd referencedisplay. In this example, the Time/Div knob has been set to 200 us/div, as indicated at the top of the display. Since the period of the signal is just slightly over 4 divisions, the period of the signal is about (200 us/div) * (4 div) = 800 us so the frequency is approximately 1/(800 us) = 1250 Hz. This measurement agrees with the label on the front panel that indicates that the calibration signal should be ≈1.2 kHz. Again, the Trigger Mode should be Auto or Auto Lvl and the mode should be RUN. The Trigger controls allow you to stabilize periodic waveforms on the screen and capture single-shot waveforms. You use the Trigger controls to select the slope and voltage level of a particular signal used as the trigger signal. When this trigger signal matches the settings, the oscilloscope will trigger a sweep of the cathode-ray tube across the display screen, displaying a single trace of the input signal. Since the trigger occurs on a certain voltage level of either a rising or falling edge, a periodic signal can be displayed as a stationary pattern. Trigger SOURCE – The oscilloscope does not necessarily have to trigger on the signal being measured, although this is the most common source. The Trigger Source can be channel 1, channel 2 or an External Trigger input signal. Trigger MODE – The trigger mode determines when the oscilloscope draws a trace. Normal mode: the oscilloscope only sweeps (draws a new trace) when the trigger signal reaches the set trigger point. If the trigger point is not reached, no trace is drawn. Therefore, you would not want to use Normal mode triggering to measure a DC signal because the oscilloscope would never sweep. Auto mode: the oscilloscope “free runs”, meaning that it sweeps even if the trigger point is not reached. This is the mode which should be used for measuring DC signals. Auto Lvl: the oscilloscope resets the trigger level to the center of the signal. Single: the oscilloscope only triggers one single-sweep the first time the trigger point is reached. Trigger Slope: The slope setting determines if the trigger occurs on a rising or falling edge. In Figure 2, the scope is set to trigger on a rising edge, as shown by the up-arrow at the top-right corner of the display. Trigger Coupling: Just as an input signal can be AC or DC coupled, the trigger signal can also be AC or DC coupled. (A DC coupled signal retains the DC offset, while an AC coupled signal has the DC component filtered out.) In addition there are special settings for rejecting low frequencies (LF), high frequencies (HF) and rejecting noise. Trigger Level: This knob adjust the voltage of the trigger point. Trigger Holdoff: This knob keeps the trigger from re-arming for some amount of time. This can be used to stabilize complex waveforms. The Holdoff range is from 200ns to about 13.5 s. Unless you are trying to measure very complex waveforms, you will probably not need to use this knobII. The HP 6205B Dual Power Supply Figure 3. The HP 6205B dual power supply front panel The HP6025B dual DC power supply consists of two identical, independently-controlled power supplies. Each power supply can provide either 0-40 Volt output at 300 mA or 0-20 Volt at 600 mA, as indicated at the top of the front panel above the meters. The maximum output voltages (40V or 20V) are independently selected using the front panel RANGE switches. Both of the power supplies have separate VOLTAGE controls, which consist of an outer knob for coarse control and an inner knob for fine control. Both power supplies have their own front panel meter which can be used as either a 0-5V or a 0-50V voltmeter or as a 0-0.75A or a 0-0.075A