Specifications
56
Oscilloscope safety
Remember that your safety (and often the safety of others working near you) is ultimately your
responsibility. Take this responsibility seriously and be methodical about it. Don't engage in horseplay.
Use checklists to remind you of things that need to be done. The cost and effort of safety training and
practicing its rules will seem like a trivial expense compared to the human cost of an accident or a
death after the fact.
1. Don’t expose high voltages needlessly in the equipment under test. Remove housings and
covers only when necessary. Turn off equipment while making test connections in high-voltage
circuits. Discharge high-voltage capacitors after removing power.
2. If possible, familiarize yourself with the equipment being tested and the location of its high
voltage points. However, remember that high voltage may appear at unexpected points in
defective equipment.
3. Use an insulated floor material or a large, insulated floor mat to stand on, and an insulated work
surface on which to place equipment; make certain such surfaces are not damp or wet.
4. Use the time-proven “one hand in the pocket” technique while handling an instrument probe. Be
particularly careful to avoid contacting a nearby metal object that could provide a good ground
return path.
5. When using a probe, touch only the insulated portion. Never touch the exposed tip portion.
6. When testing ac powered equipment, remember that ac line voltage is usually present on some
power input circuits such as the on-off switch, fuses, power transformer, etc. any time the
equipment is connected to an ac outlet, even if the equipment is turned off.
7. Some equipment with a two-wire ac power cord, including some with polarized power plugs, is
the “hot chassis” type. This includes most recent television receivers and audio equipment. A
plastic or wooden cabinet insulates the chassis to protect the customer. When the cabinet is
removed for servicing, a serious shock hazard exists if the chassis is touched. Not only does
this present a dangerous shock hazard, but damage to test instruments or the equipment under
test may result from connecting the ground lead of most test instruments to a “hot chassis”. To
make measurements in “hot chassis” equipment, always connect an isolation transformer
between the ac outlet and the equipment under test. To be on the safe side, treat all two wire ac
powered equipment as “hot chassis” unless you are sure it has an isolated chassis or an earth
ground chassis.
8. Never work alone. Someone should be nearby to render aid if necessary. Training in CPR
(cardiopulmonary resuscitation) first aid is recommended.
9. Use shrouded BNC coaxial cables if possible. Unshrouded BNC connectors may have
significant voltages on the outside metal, especially on instruments that use floating BNC
connections.
10. Know about Category ratings (see CAT I in the glossary) and how they apply to your scope and
probes. Don't use these measurement tools on circuits that require higher category ratings than
your scope and probes provide.
Preventing damage to the oscilloscope
1. On an analog oscilloscope, don’t leave the oscilloscope set at high brightness for long intervals.
A bright spot or line left in one position can permanently burn the CRT's phosphor.
2. Keep the ventilation holes clear.
3. Avoid dusty environments or spilling liquids onto the oscilloscope.
4. Don’t apply excessive voltage to the scope’s input jacks. Voltage limits are clearly stated in your
operating manual and usually on the scope itself.
5. Connect the ground clip of a scope probe only to earth ground or isolated common in the
equipment under test.
6. Keep the scope away from direct sunlight, high temperature/humidity, mechanical vibration,
electrical noise, and strong magnetic fields.
All content Copyright © B&K Precision Corporation, except where otherwise noted.
Copying/reprinting/republishing without express written consent prohibited.