United Process Versapro, Руководство по установке и эксплуатации

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VersaPro Temperature Controller Page 9
Copyright © 2013, United Process Controls Inc.
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2.9 Voltage rating
The maximum continuous voltage applied between any of the following terminals must not exceed 250VAC:

line or neutral to any other connection;

relay output to logic, dc or sensor connections;

any connection to ground.
The controller should not be wired to a three phase supply with an unearthed star connection. Under fault
conditions in this supply could rise above 264VAC with respect to ground and the product would not be safe.
Voltage transients across the power supply connections, and between the power supply and ground, must not
exceed 2.5kV. Where occasional voltage transients over 2.5kV are expected or measured, the power
installation to both the instrument supply and load circuits should include a transient limiting device.
These units will typically include gas discharge tubes, metal oxide varistors, and constant voltage transformers
help suppress voltage transients on the supply line due to lightning strikes or inductive load switching. Devices
are available in a range of energy ratings and should be selected to suit conditions at the installation.
2.10 Conductive pollution
Electrically conductive pollution must be excluded from the cabinet in which the controller is mounted. For
example, carbon dust is a form of electrically conductive pollution. To secure a suitable atmosphere in
conditions of conductive pollution, fit an air filter to the air intake of the cabinet. Where condensation is likely,
for example at low temperatures, include a thermostatically controlled heater in the cabinet.
2.11 Over-temperature protection
When designing any control system it is essential to consider what will happen if any part of the system should
fail. In temperature control applications the primary danger is that the heating will remain constantly on. Apart
from scrapping the product, this could damage any process machinery being controlled or even cause a fire.
Reasons why the heating might remain constantly on include:

the temperature sensor becoming detached from the process;

thermocouple wiring becoming a short circuit;

the controller failing with its heating output constantly on;

an external valve or contactor sticking in the heating condition;

the controller setpoint set too high.
Where damage or injury is possible, we recommend fitting a separate over-temperature protection unit. Factory
Mutual requires that any over temperature device use an independent temperature sensor, which will isolate
the heating circuit.
Please note that the alarm relays within the controller will not give protection under all failure conditions. This
instrument is not suited for over temperature protection and should not be used as a safety device.