Rockwell Automation Safety Guidelines for the Application, Installation, and Maintenance of Solid-State Control - Manual (Page 21)

Publication SGI-1.1 - August 2009
Section 4: Installation Guidelines 21
4.4 Compatibility of Devices
with Applied Voltages and
Frequencies Prior to energization, users and installers should verify that the applied voltage
and frequency agree with the rated voltage and frequency specified by the
manufacturer.
NOTE: Incorrect voltage or frequency may cause a malfunction of, or
damage to the control.
4.5 Testing Precautions When testing solid-state control, the procedures equipment should be
electrically equivalent to that recommended by the manufacturer for the test
procedure. A low impedance voltage tester should not be used.
High voltage insulation tests and dielectric tests should never be used to test
solid-state devices. If high voltage insulation of field wiring is required,
solid-state devices should be disconnected. Ohmmeters should only be used
when and as recommended by the equipment manufacturer.
Testing equipment should be grounded; if it is not, special precautions should
be taken.
Comments: 4.5 —Testing Precautions
Make-do test devices such as incandescent lamps or neon lamps should
not be used for checking voltages in solid-state systems. Incandescent
lamps have low impedance; the low impedance of these devices can
effectively change a voltage level from a logic "1" condition to a logic "0"
condition when attempting to make a measurement. Unexpected machine
motion can result if an output to a controlled device is energized as a
result. Neon lamps do not respond to voltages typically used in logic
circuits (e.g., 32V DC or less). Use of a neon lamp tester could lead to false
conclusions about the voltage level present in a circuit.
High input impedance meters are required to obtain accurate voltage
measurements in high impedance circuits. Unless otherwise specified by
the manufacturer, a meter with an input impedance of ten megohms or
greater is recommended for making voltage measurements. The meter
must also have sufficient sensitivity to measure logic level voltages; some
meters do not respond to low voltages.
4.6 Startup Procedures Checks and tests prior to startup and startup procedures recommended by the
manufacturer should be followed.
Comments: 4.6 —Startup Procedures
Startup procedures can provide important benefits for safety with new
installation, or after modifications or repairs. A "dry run" under controlled
conditions can verify proper installation and functioning of the control
system before it is turned over to operating personnel.
Many programmable solid-state systems have the capability for simulating
operation in a mode known as "test" mode or "dry run" mode. These
modes allow a user to check a program and correct obvious programming
errors with outputs disabled. Unexpected machine motion and possible
damage to workpieces and equipment is thus avoided. These modes can
also be used to verify proper system operation after a repair.