The TP48 range of surge protection devices uniquely provide a level of protection for 2, 3 and 4 wire field-mounted transmitters that is far in excess of the optional transient protection facilities available from transmitter manufacturers – without involving any additional wiring, conduit modifications or other expensive extras.

The TP48 range protection network consists of high-power, solid-state electronics and a gas-filled discharge tube capable of diverting 20 kA surge impulses. The complete unit is housed in a robust 316 stainless steel enclosure, threaded to suit the most common conduit entries used on process transmitters.

Available versions include:

• 1/2” NPT

• 20 mm ISO

• G1/2” (BSP 1/2 inch)

Installation can easily be carried out retrospectively on existing installations. The TP48 is simply screwed into any unused conduit entry on the transmitter housing, and flying leads are connected to the transmitter terminal block (+ve, -ve) and the internal earth stud.

Protection coverage depends on the wiring configuration:

• 3-wire TP48 protects +ve, -ve and signal

• 4-wire TP48 protects +ve, -ve, signal +ve and signal -ve

The TP48 operates transparently, passing AC or DC signals without attenuation while safely diverting surge currents to earth and clamping output voltages to defined safe levels. Normal transmitter operation is not affected in any way.

Earthing is achieved directly through the local transmitter casing, eliminating the need for a separate earth conductor or ground stake at the transmitter. This ensures that transmitter electronics are never exposed to damaging transient voltages between lines or between lines and earth.

Any surge current appearing as either a series-mode or common-mode transient is converted into a common-mode voltage. The transmitter electronics are temporarily raised to a higher potential and then automatically return to normal operating voltage without damage.

For hazardous area applications, approvals are available for both intrinsically safe and flameproof (explosion-proof) installations, covering all gas groups and temperature classes up to:

• T4 for TP48 3-wire and 4-wire versions

• T6 for TP48 versions

Where transmitters are installed in circuits suitable for Division 2 / Zone 2 locations, the TP48 can be added without adversely affecting the overall safety level of the system.

For fieldbus applications, the TP32 should be used. The TP32 complies with IEC 61158-2:2004 and ANSI/ISA-50.02-2:1992 requirements for 31.25 kbit/s systems such as:

• FOUNDATION™ Fieldbus

• PROFIBUS-PA

• WorldFIP