Using the Hitachi oscilloscope
The instrument is a fairly ancient model, but works quite well once you know how to do it. Its main defect is that we seem to have lost the manual, so there is an element of guesswork in driving it. It is also inconvenient that it doesn't have a persistent display, so it's only useful for repetitive signals; in pracice, that isn't much of a problem for our purposes. This description treats it as a double channel split-beam oscilloscope, though it can do more.
You will usually find one or two probes attached to the sockets on the front panel. These make the connection with the system you will measure. Notice that each is provided with an earth clip as well as a measuring connection; that's because the electronics of each channel are isolated from any direct connection with earth so that they can be used at arbitrary voltages.
There are several probes, suitable for making different sorts of connection. ( They should be in a box on top of the cupboard beneath the workbench. ) Many have switches with which you can change their sensitivity; if you want the oscilloscope display to be correct according to the supposed volts per centimetre on the Y scale, choose the x1 position.
Turn on the mains switch, and turn on the oscilloscope by pressing the POWER button at the bottom left corner of the front panel. An indicator light should come on, and activity might, or might not, be visible on the screen after a few seconds.
Before switching off, it is kind to reset the machine to a simple state; even if you know what you're doing, the next person to use it might not. Single-channel operation with channel 1 displayed is sensible; press CH1 below ADD on the VERT MODE panel. Switch off on the front panel and the mains.
Use channel 1 : press the CH1 button below ADD in the VERT MODE panel. Set the CH1 switch above the channel 1 probe INPUT socket to GND; that guarantees zero deflection voltage on the channel 1 input. Adjust the INTENSITY A&B knob for clear but not dazzling brightness. If you see nothing at all, it might be that someone set the vertical displacement very high or low ( adjust with CH1 POSITION ) or a horizontal displacement off the screen ( adjust with the POSITION knob ). Fiddle about until you find a trace on the screen ( if you have difficulty, try pressing TRACE FINDER beneath the screen ), or decide that something has gone wrong.
Use the CH1 POSITION control to set the vertical displacement to wherever you want it - usually, though not necessarily, with zero input voltage ( with the selector switch at GND ) placing the trace on the horizontal axis in the centre of the screen. Don't forget to switch CH1 to the signal ( usually DC ) before trying to measure it.
The vertical sensitivity is set by adjusting the channel 1 VOLTS/DIV knob. The values available lie in the range 5mV to 5V per screen division; around 1V to 5V is usually about right for the things you might do in the laboratory.
The scanning speed is set by adjusting the TIME/DIV knob. Unless you know fairly precisely what you'll want, it's usually easiest to start by connecting the signal with a slow scan speed, and then to increase the speed until the features you want become visible.
You can shift the trace horizontally using the POSITION knob. It's easiest to make this adjustment if you can see the whole trace at once; use a fairly fast scan - say, 1mS per division.
Leaving the scan free-running is useful for exploring and getting a general idea what's happening, but to measure signals it's usually necessary to control where they appear on the screen so that you can get a reproducible and static display.
The oscilloscope is equipped with a trigger mechanism to help with this control. The principle of the trigger is that the sweep across the screen is started when some recognisable feature of an input signal ( commonly, though not necessarily, a signal displayed on the screen ) is detected. The feature used is usually the signal's passing a certain preset voltage in either the increasing or decreasing direction - so, for example, the feature chosen might be an increasing change past -2V.
The trigger controls are at the right-hand side of the front panel. There are button controls to select the sort of triggering required and the source of the trigger signal, and a rotary control to adjust the trigger voltage.
By connecting another signal to a probe attached to channel 2 you can display or compare two signals on the oscilloscope screen. The simplest way to use two channels is to display either one or the other; you can do that by pressing either CH1 or CH2 beneath the ADD in the VERT MODE panel.
It is more useful to show two signals at once so that you can compare them directly. You can do that using CHOP or ALT on the VERT MODE panel. CHOP switches the oscilloscope beam vertical deflection rapidly between the two channels so that two traces are effectively drawn at once within the same scan. This is likely to be sufficient for any work you will want in the course, but if the switching speed is inconveniently low you can use ALT to display complete scans from the two channels alternately.
Alan Creak,
January, 1998.
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