Table II. Summary of NEMA Instrument Enclosure Designations 1 Description
1
Indoor
General purpose
Accidental contact with enclosed equipment, falling dirt
2
Indoor
Drip-proof
Accidental contact with enclosed equipment, falling dirt, falling liquids, light splashing
11
Indoor
Corrosionresistant, drip-proof
Accidental contact with enclosed equipment, falling dirt, falling liquids, light splashing, corrosive agents
12
Indoor
Dust-tight, drip-tight
Accidental contact with enclosed equipment, falling dirt, falling liquids, light splashing, dust, lint, fibers, flyings, oil or coolant seepage
13
Indoor
Oil-tight, dust-tight
Accidental contact with enclosed equipment, falling dirt, falling liquids, light splashing, dust, lint, fibers, flyings, oil or coolant seepage, oil or coolant spraying, splashing
Indoor or outdoor
Watertight, dust-tight, sleet-resistant
Accidental contact with enclosed equipment, falling dirt, falling liquids, I ight splashing, dust, lint, fibers, flyings, windblown dust, hosedown, splashing water, rain, snow, sleet
Indoor or outdoor
Watertight, dust-tight, sleet-resistant corrosionresistant
Accidental contact with enclosed equipment, falling dirt, falling liquids, light splashing, dust, lint, fibers, flyings, windblown dust, hosedown, splashing water, rain, snow, sleet, corrosive agents
Indoor or outdoor
Submersible, watertight, dust-tight
Accidental contact with enclosed equipment, falling dirt, falling liquids, light splashing, dust, lint, fibers, flyings, windblown dust, hosedown, splashing water, rain, snow, sleet, occasional submersion (30 min duration)
Outdoor
Rain-tight, sleet-resistant
Windblown dust, rain, snow, sleet
3R
Outdoor
Rainproof, sleet-resistant
Accidental contact with enclosed equipment, rain, snow, sleet
3S
Outdoor
Dust-tight, rain-tight, sleetproof
Accidental contact with enclosed equipment, windblown dust, rain, snow, sleet
The next generation of continuous f l o w analyzers is here. 4X
Breda FIA The Breda on-line automatic Flow Injection Analyzer (FIA) offers a number of important advantages over the traditional air segmented analyzer. These include · higher sample throughput · no sample carryover · no air bubbles t o introduce and remove · simpler, less costly instrumentation. Key applications are in the areas of • food a n d beverage control
Environmental Conditions
Location
NEMA Type
1
Technical Information Tl 7-1g, The Foxboro Co., Foxboro, Mass.
• water management • industrial chemistry • agriculture • public health and • industrial process control Send for details.
BREDA INSTRUMENTS Serving the analytical chemist since 1960. One Sutter Street, San Francisco, CA 94104, USA, (415) 788-4120 Telex 278 227 (UNICO) Konijnenberg 40, 4800 DH Breda, Netherlands (76) 877750, Telex 54 197 (Cenco NL) CIRCLE 27 ON READER SERVICE CARD
ratory instruments m u s t be designed to be versatile and to cover a wide range of sample levels. T h i s results in instruments with many features a n d additional levels of complexity. In t h e process situation, t h e n a t u r e of t h e sample a n d its range are well established a t t h e time of installation. T h e process i n s t r u m e n t manufacturer can t r a d e off versatility and range for simplicity, ease of maintenance, and ruggedness. Sampling A new process i n s t r u m e n t is usually "checked" by comparing its readings
1258 A · ANALYTICAL CHEMISTRY, VOL. 52, NO. 12, OCTOBER 1980
with laboratory analyses. Often they do not agree. One of t h e reasons lies in the n a t u r e of sampling as done for t h e laboratory and as done in t h e plant. T h e laboratory has t h e advantage t h a t it can do many analyses on t h e same sample, a n d t h u s is able t o establish i n s t r u m e n t precision and reproducibility. And because its instruments are well-calibrated a n d cared for, it has great confidence in t h e results. However, t h e laboratory is often unaware of t h e problems of obtaining a representative "correct" sample. As a result, t h e laboratory assumes t h a t it has obtained t h e right sample, a n d
