Instruction; Overview; Features And Benefits; Electrical Characteristics - Honeywell STT25D Operator's Manual

APPENDIX A
A.1

Overview

Honeywell's transient protectors external to housings (part number 30755970-501) are
designed to protect STT 3000 transmitters from damaging transients induced by
lightning or heavy electrical equipment.
Transient protectors divert induced surge current around the transmitter. This reduces
the voltage potential between the housing and the internal electronic components from
several thousand volts to a low and safe level.
A.2

Features and Benefits

The weatherproof transient protectors are sealed in epoxy in a ½ inch stainless steel
pipe nipple. This is done to ensure that their performance is not affected by severe
environmental conditions.
Other benefits of transient protectors are:
•
Two stage protection,
•
A common chamber, three-element, gas tube which assures ultra-fast and
balanced clamping,
•
A solid-state portion which holds the clamping voltage at a very low, safe level,
•
Symmetric construction which assures equal performance in either polarity in
surges or loop current.
A.3

Electrical Characteristics

Table A.1 lists the electrical characteristics of transient protectors.
Compatibility
Supply voltage
Resistance to loop added
DC clamping level
Impulse clamping level L-L
500A, 10 x 1,000 µs
Surge
Smart Temperature Transmitter STT250 – Operator Manual
TRANSIENT PROTECTOR
INSTALLATION INSTRUCTION
Table A-1 Electrical Characteristics
Parameter
L-L (line to line)
L-G (line to ground)
L-G
Specification
4-20 mA loops
28 Vdc maximum
44 ohms
36 V ± 10%
200 to 350 V
50V maximum
800 to 1000 V
400 Min.
33