Vaisala HMT360Series Guide de l'utilisateur télécharger pdf (Page 40)

User’s Guide ______________________________________________________________________

38 ___________________________________________________________________ M010056EN-J

If assuming that the operating voltage would be ≥ 24 V, the maximum

acceptable voltage drop U

drop

in cables is:

drop

= U

- U

min

drop

= 14 V - 12 V = 2 V

We also know that:

out

= 20 mA

and that total resistance of the cable R

cabletot

is cable resistance R

cable

multiplied with the total maximum length of the cables l

max

cabletot

= R

cable

× l

max

From these facts the following equation can be formed:

drop

= R

cabletot

× I

out

2 = 2 × 0.085 Ω/m × l

max

× 20 mA

max

= 2 V / (20 mA × 2 × 0.085 Ω/m)

max

= 588 m = 1930 ft, maximum cable length.

NOTE

If longer cable length is required, use of the galvanic isolators is

recommended if possible.

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Vaisala HMT360Series Guide de l'utilisateur Page 40