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SM Surge Rev 2
1 Introduction
1.1 Application and function
The products concerned in this manual are ‘Surge Protection’ devices which can be located in safe or hazardous
areas of a process plant to guard against the direct and indirect effects of lightning, or other transient overvoltage,
on the instrumentation and power signals. They are also designed and tested according to IEC 61643-21 (Low
voltage surge protective devices) for use in signal and communication loops.
The location, or mounting, of the surge protection device is a key parameter when considering the operation
of the device and the consequences of breakdown or failure upon the operation of the signal loop to which it
is connected.
The TP family of products are designed to protect field-mounted equipment, such as process measurement
transmitters for level, flow, pressure, etc, by fixing directly into the cabling conduit entries of the housing. The
SD, SLP and IOP range are mounted on DIN rail in a cabinet or enclosure to protect the measuring and control
equipment that is usually located in a control or equipment room.
Each module provides a hybrid surge protection circuit for one or two instrument loops. The devices are passive
and consume no loop current in normal operation.
There are no configuration switches or operator controls to be set on the modules – they perform a fixed function,
related to the model selected, and can be considered as wiring components that pass the process signals without
alteration.
Note:
The information given in this manual is intended to assist in the selection and application of surge
protection devices for instrumentation signals that are being used to provide functional safety according to the
latest IEC 61508 and IEC 61511 standards.
Within the context of these standards the surge protection devices themselves do not perform a defined safety
function and thus a full assessment for functional safety to IEC 61508 would not be relevant. The products are
regarded as wiring components, providing connection and termination for the electrical signals, with the key
concern being the reliability of the signal transfer through the device.
See Appendix B where this position is affirmed by a notified certification body.
1.2 Variant Description
Functionally the surge protection devices are essentially the same, within a given range, but the modules differ in
the maximum signal voltage they will conduct in normal operation.
The TP items become an integral part of the field transmitter and the SD/SLP/IOP models are selected to suit the
specific requirements for protection of one or more process loops.
Surge protectors range
