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