The problem this telephone solves is not being able to hear the telephone. In a refinery,
a compressor house or a process area, a ringing telephone is inaudible, so calls are missed -
and on a hazardous site the call being missed may be the one that mattered. The KNEx6 deals
with it by being loud and by being visible: ringing is quoted at over 100 dB(A) at 50 cm,
there is a built-in 8 ohm 0.5 W sounder with a flash light, and it supports connection of an
external explosion-proof horn of 8 ohms rated from 5 to 30 W for areas where even that is not
enough.
That external horn connection is the feature that distinguishes this from an ordinary Ex
telephone. It means one certified telephone can serve a genuinely loud area, with the horn
mounted where it will be heard rather than being limited to whatever fits on the telephone
itself. The interface provides for the handset, a D20 ringtone at 8 ohm 0.5 W, an LED at
5 V DC 0.75 W, and the explosion-proof horn, on an optional eight-core cable.
On certification, the stated protection type is II 2G Ex db ib IIB T5 Gb with a temperature
range of -20 to 55 degrees C, and KNTECH describe the range for use in Zone 1 and Zone 2, with
Ex II 2 GD covering dust as well as gas. The combination of db - flameproof enclosure - with
ib - intrinsically safe circuits - is a common and sensible arrangement for a telephone: the
enclosure contains any incident while the circuits themselves are energy-limited. IIB is a gas
group, and it is worth checking against your area classification, because IIB does not cover
IIC gases such as hydrogen and acetylene. We confirm the marking on the certificate for the
variant supplied against your classification drawing before quoting.
Mechanically it is a substantial object - die-cast aluminium alloy, 345 x 262 x 161 mm and
10.65 kg without the speaker and light, IP66, powder coated in UV-stabilised polyester, with
vandal and tamper-resistant hardware and a self-closing door cover. The keypad is stainless
steel, waterproof and dustproof, the hook-switch is a magnetic reed type, and the heavy-duty
handset has a hearing-aid compatible receiver and a noise-cancelling microphone on an
industrial curly cord. It runs from AC 110 V or AC 220 V, dials DTMF, stores ten speed-dial
groups, and KNTECH quote MTBF at 100,000 hours.
KNEx6 sits in a family, and the alternatives are worth knowing: KNEx5 is another analogue
Ex telephone, KNEx7 is an IP version and KNEx8 is VoIP. Where a site is standardising on IP
telephony, those are the ones to look at rather than adding analogue infrastructure for the
hazardous areas alone.
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