Yokogawa MLX - Manual (Page 10)

Page 10 of 49
IM 60A02S01-01E-A
(4) Ambient Atmosphere
(5) Do not install the indicator in a corrosive atmosphere. If this cannot be avoided, there
must be adequate ventilation as well as measures to prevent the leaking of rain water and
the presence of standing water in the conduits.
(6) Shock and Vibration
(7) Although the MLX is designed to be relatively resistant to shock and vibration, an
installation site should be selected where this is kept to a minimum.
2.5 Insulation Resistance and Dielectric Strength Test
Since the MLX has undergone insulation resistance and dielectric strength tests at the factory
before shipment, normally these tests are not required. If the need arises to conduct these tests,
heed the following:
(1) Do not perform such tests more frequently than is absolutely necessary. Even test
voltages that do not cause visible damage to the insulation may degrade the insulation
and reduce safety margins.
(2) Never apply a voltage exceeding 500 V DC (100 V DC with an internal lightning protector)
for the insulation resistance test, nor a voltage exceeding 500 V AC (100 V AC with an
internal lightning protector) for the dielectric strength test.
(3) Before conducting these tests, disconnect all signal lines from the transmitter terminals.
The procedure for conducting these tests is as follows:
• Insulation Resistance Test
(1) Short-circuit the + and – SUPPLY terminals in the terminal box.
(2) Turn OFF the insulation tester. Then connect the insulation tester plus (+) lead
wire to the shorted SUPPLY terminals and the minus (–) lead wire to the grounding
terminal.
(3) Turn ON the insulation tester power and measure the insulation resistance. The
voltage should be applied as briefly as possible to verify that the insulation
resistance is at least 20 MΩ.
(4) After completing the test and being very careful not to touch exposed conductors
disconnect the
insulation tester and connect a 100 kΩ resistor between the
grounding terminal and the short-circuiting SUPPLY terminals. Leave this resistor
connected at least one second to discharge any static potential. Do not touch the
terminals while it is discharging.
• Dielectric Strength Test
(1) Short-circuit the + and – SUPPLY terminals in the terminal box.
(2) Turn OFF the dielectric strength tester. Then connect the tester between the
shorted SUPPLY terminals and the grounding terminal. Be sure to connect the
grounding lead of the dielectric strength tester to the ground terminal.
(3) Set the current limit on the dielectric strength tester to 10mA, then turn ON the
power and gradually increase the test voltage from ‘0’ to the specified voltage.
(4) When the specified voltage is reached, hold it for one minute.
(5) After completing this test, slowly decrease the voltage to avoid any voltage surges.