Vaisala HMT360N - Manual (Page 39)

Chapter 3 _______________________________________________________________ Installation
VAISALA _______________________________________________________________________ 37
Maximum Cable Resistance Calculation for the
Barrier (Vaisala Order Code: 210664)
Calculation of the maximum cable length from barrier to
transmitter:
If assuming that the operating voltage would be
 24 V, the maximum
acceptable voltage drop U
drop
in cables is:
U
drop
= U
S
- U
min
U
drop
= 14 V - 12 V = 2 V
We also know that:
I
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
:
R
cabletot
= R
cable
× l
max
General specifications of HMT360:
Supply voltage U
in
= 24 V (12 ... 35 V)
Maximum current I
out
= 20 mA
Minimum operating voltage for
HMT360 U
min
= 12 V (15 V with serial port)
Stahl 9001/51-280-091-141 (values taken from the specifications):
Rated operating voltage U
N
= 20 ... 35 V
Transmitter supply voltage U
S
= U
N
- 9.5 V, when
U
N
 23.5 V
or U
S
= 14 V, when U
N
 23.5 V
Maximum load R
L
 350 
Cable resistance (as an example) R
cable
= 0.085
/m/core (2 ×
0.085
/m/pair)