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design of the instrument and scale system. If a Electrostatic discharge
reaches the instrument, an alternate ground path must be provided that does not
include the sensitive electronics of the instrument. To facilitate this
alternate ground path, PROPER GROUNDING IS ESSENTIAL! A thick,short ground
cable connected directly to a ground rod or similar direct earth ground is
necessary for proper protection. The 200 feet of 18 gauge wire used in the
earth ground circuit of most three prong plugs is not adequate to dissipate the
nano-second rise times of ElectroStatic Discharge pulses.
Proper shielding of all interconnect cables is also required. Connect the
shield, preferably at the load cell or receiving end. NEVER CONNECT THE SHIELD
AT BOTH ENDS. Connecting the shield at both ends causes ground currents to
flow in the shield, which can create ground loop problems.
AC power
Before continuing with the Electrostatic Discharge(ESD) solution, lets discuss
power for a few paragraphs. Many times ESD is blamed for damage that is
actually due to line power problems. Surges and sags in the average 110 volt
ac power line are very common, and heavy industrial use only makes the power
"dirtier". If you suspect power problems, there are many good products on the
market to "clean up" your ac power. The XC780 has been tested to withstand
6000 Volts of standard line transient, which should be more than enough for the
average user. However, some industrial locations may generate larger non-
standard transients and lightning is always a possibility, so certain
applications may still require transient suppression.
1.
Surge Suppressors- These devices absorb the energy of a large
voltage surge on the power line before it reaches the instrument. They are
effective for large industrial line spikes or lightning.
2.
Voltage Regulators- Voltage regulators will maintain a constant
voltage output with varying voltage inputs. Most also contain surge
suppressors. These are effective for power brownouts(when the 110 ac line
voltage drops).
3.
Uninteruptable Power Supplies(UPS)- UPS devices will always
maintain power to the instrument. In the event of power failure, a battery in
the UPS powers the output until an orderly shutdown can be performed. Most
UPSs also contain surge suppressors. This type of device is used in critical
applications where the instrument cannot be allowed to shut down, even if the
power does. The XC780 Battery Operation option provides a similar function.
Selecting the right power protection components for your application requires
careful consideration. If unsure of your requirements, contact your dealer or
Sterling Scale for assistance.
Static Protection for the XC780:
