8.13.
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295
havior of any one of these circuits can be assessed at a glance. An "electron ray, indicator type" tube (6E5) can be substituted cheaply for an
oscilloscope tube if used with a simple amplifier, and its rapid response
to fluctuations by visible flickering will give most of the information that
might be desired [Bishop, F. W. (1953) Electronics,
26]. The custom design, construction, and installation of such equipment, however, is apt
to require the services of an electronics engineer, and most laboratories
will not wish to go to the trouble and expense. The Canal Instrument
Company of Bethesda, Maryland, is marketing a power monitoring system which is adaptable to several of the commercial microscopes. Although the system seems cumbersome and its usage overly technical for
common checking, it will serve the person with some knowledge of
electronics fairly well, and be quite useful in case of serious trouble.
Most laboratories, however, will not be prepared to explore electronic
difficulties very deeply, and no doubt will call in the service representative when these arise. Before taking the microscope out of service, however, there are several things that the investigator should think of and
check, for he may be able to take care of the difficulty quickly himself.
First, the sliding potentiometers attached to the control knobs get dirty
and establish current leakage paths so that they cease to regulate circuits
smoothly. A particularly common difficulty is to have an oscillatory makeand-break instability between one turn of the resistance wire and the
next, so that a small circuit fluctuation is set up. This often is just
enough to be quite damaging to image stability at high magnifications
if it involves the focusing controls of the objective lens. When focusing
is completed, one can tap the controls lightly with the fingertips to be
sure that the image is stable. When the potentiometers become dirty
in this manner they can be temporarily repaired by cleaning them with
organic solvents and, perhaps by using a fine abrasive cloth or paper. But
the best solution is to buy new potentiometers which, in any case, will
have to be done shortly.
Dirty switch and plug connections are in somewhat the same category
as dirty potentiometers and may produce oscillating or irregular instabilities in the circuits in which they are involved. It is easy to turn
panel switches on and off a few times to wipe their contacts, and it is
not difficult to pull and reset column plugs two or three times to clean
their prongs and sockets.
A common cause of electrical instability that is easily taken care of
is battery "noise." In microscopes which use dry cell batteries for voltage
INSTRUMENT STABILITY
295
havior of any one of these circuits can be assessed at a glance. An "electron ray, indicator type" tube (6E5) can be substituted cheaply for an
oscilloscope tube if used with a simple amplifier, and its rapid response
to fluctuations by visible flickering will give most of the information that
might be desired [Bishop, F. W. (1953) Electronics,
26]. The custom design, construction, and installation of such equipment, however, is apt
to require the services of an electronics engineer, and most laboratories
will not wish to go to the trouble and expense. The Canal Instrument
Company of Bethesda, Maryland, is marketing a power monitoring system which is adaptable to several of the commercial microscopes. Although the system seems cumbersome and its usage overly technical for
common checking, it will serve the person with some knowledge of
electronics fairly well, and be quite useful in case of serious trouble.
Most laboratories, however, will not be prepared to explore electronic
difficulties very deeply, and no doubt will call in the service representative when these arise. Before taking the microscope out of service, however, there are several things that the investigator should think of and
check, for he may be able to take care of the difficulty quickly himself.
First, the sliding potentiometers attached to the control knobs get dirty
and establish current leakage paths so that they cease to regulate circuits
smoothly. A particularly common difficulty is to have an oscillatory makeand-break instability between one turn of the resistance wire and the
next, so that a small circuit fluctuation is set up. This often is just
enough to be quite damaging to image stability at high magnifications
if it involves the focusing controls of the objective lens. When focusing
is completed, one can tap the controls lightly with the fingertips to be
sure that the image is stable. When the potentiometers become dirty
in this manner they can be temporarily repaired by cleaning them with
organic solvents and, perhaps by using a fine abrasive cloth or paper. But
the best solution is to buy new potentiometers which, in any case, will
have to be done shortly.
Dirty switch and plug connections are in somewhat the same category
as dirty potentiometers and may produce oscillating or irregular instabilities in the circuits in which they are involved. It is easy to turn
panel switches on and off a few times to wipe their contacts, and it is
not difficult to pull and reset column plugs two or three times to clean
their prongs and sockets.
A common cause of electrical instability that is easily taken care of
is battery "noise." In microscopes which use dry cell batteries for voltage