Choice of the length of cable
Selection of protection grand
According to China's standard GB 4208-84(equivalent to IEC529-76), THE protection grand of out-housing case is divided into following grands:
IP65 is spraying-water proof grand and allows spraying flowmeter with water in all direction (spraying water pressure is 30KPa(0.3bar)), flow is 12.5Litter/min, the distance between spraying nozzle and meter is 3 meter.IP67 is immersion proof grand and allows immersing flowmeter to 150 cm underwater for lasting over 30 minutes.IP68 is submersion roof grand and allows flowmeter operating underwater for long time. The max. submerged depth is determined by manufacturer and customer.
In accordance with requirements as above and actual work condition for flowmeter that is the principle for selecting protection grand. If flowmeter is underground and submerged usually, the best choice of protection grand is IP68. If the flowmeter is on the ground, the better choice is IP65.
Selection of earthing ring
If the process pipe connected with flow meter (being related to measured flow media) is insulated, selecting general and PVC model earthing ring is necessary. The earthing ring material is corresponding to corrosion of measured flow media.
If the measured media is strong abrasion, the better choice is earthing ring with neck for protecting lining of input & output terminal & lasting its life.
Selection of the length of cable
Max. length Lmax) concerned with the relationship among the single cable, exciting cable and media conductivity could be shown by following curve drawing
To select YZ medium size rubber cable is for exciting cable. The shorter cable length between the max. exciting cable (¦Õ10) & max. single cable (¦Õ10) for 2-core cabtyre cable 2¡Á1 mm? (IP65,IP67) and 2-core cabtyre cable CVV2¡Á1.0 mm? is max. cable length between the transducer and cover.
For example, for general running water and raw water(CONDUCTIVITY:100-500¦Ìs/cm), you select single cable & exciting cable with area (AF=2¡Á2.5 mm?). If conductivity of water is 200¦Ìs/cm, the max. single cable length (Lmax.) is 200 m.
Output single transmission cable length
A. Output current transmission cable
The max. length of cable is decided by following formula.
Ro+R¦Ë£¼1.5k¦¸ (Output current: 10 mA)
Ro+R¦Ë£¼750k¦¸ (Output current:20 mA)
R¦Ë is sum total of input resistance of back instruments.
Ro is transmission cable resistance value.
According to the Ro value and cable's area, select the max. cable's length. In fact, the practical length of cable is the half of max. length of cable.
B. Output frequency transmission cable
For the cable with 2000pf/mm distributed capacity, the max. cable's length is 200 m.
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