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Electrical connections ________________________________________________________________
Installation in hazardous locations
US and Canadian requirements
USA (FM): Wiring for intrinsically safe operation is shown in APPENDIX 2.
Canada (CSA): Wiring for intrinsically safe operation is shown in APPENDIX 3.
European requirements
CATEGORY 1 (zone 0)
The HMT360 has to be connected to Exia-certified associated apparatus with galvanic
isolation, gas group IIB or IIC. NOTE! If both analog outputs are in use, the channel 1 (-) and
channel 2 (-) must be short circuited (see figure 4-3).
CATEGORY 2 or 3 (zone 1 or 2)
The HMT360 has to be connected either to a zener barrier or galvanic isolator NOTE! If both
analog outputs are in use with a galvanic isolator, the channel 1 (-) and channel 2 (-) must be
short circuited (see figure 4-3).
Figures 4-1 and 4-2 present examples of galvanic isolators and zener barrier connections (only
CH1 connected).
Maximum load calculation for the barrier
Always check the technical data of galvanic isolator or zener barrier to define maximum load.
If the maximum load is not included in specifications it can be determined as follows.
Example: Stahl 9002/13-280-093-00 (zener barrier)
General specifications of the HMT360
Supply voltage
Maximum current
Minimum operating voltage for HMT360
Cable resistance (as an example)
Stahl 9002/13-280-093-00 (values taken from the specifications):
Typical end to end resistance
Max. additional voltage drop (20mA)
Voltage drop
Voltage for R
l
Maximum load
Vaisala _________________________________________________________________________ 24
R
= 0.085 ohm/m/core (2*0.085 ohm
cable
Cable lenght =250 m
R
=
Ctot
R
= 340 ohm
barrier
U
= 1 VDC
add
U
= I
*(R
+ R
drop
max
Ctot
U
= U
- U
- U
Rl
in
min
drop
R
= U
/I
= 3.3 V / 20 mA = 165ohm , R
lmax
Rl
max
U
= 24 V (12...35 V)
in
I
= 20 mA (100%RH)
max
U
= 12 V (15 V with serial port )
min
2*0.085 ohm/m*250m=
) + U
= 20 mA*(45+340)ohm + 1 V = 8.7 V
barrier
add
= 24 V - 12 V - 8.7 V = 3.3 V
/m/pair)
45 ohm
< 165ohm
lmax
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