27
NT538
(ONLY FOR NT538 AD)
OUTPUT 4.20mA
It is possible to connect a displaying or acquisition device to the 4.20 mA output.
The permitted load impedance for each output is from 0 to 500 ohm.
The loop is optically isolated to guarantee the maximum immunity to interference.
The 4-20 mA signal is referred to the 0-240°C range with an accuracy of 1% of full scale value
The output can be programmed in the following modes:
1-2-3-4-5-6-7-8: the 4.20 mA output refers to the fixed channel that has been set.
SCAN: the 4.20 mA output automatically scans the active channels every 2 seconds
(default setting)
HOT: the 4.20mA output automatically refers to the hottest channel among the active ones
See steps 36 - 37 of the table on page 15.
Note: if the 4.20 output is programmed on CHn and this is disabled, the control unit will automatically set on HOT.
The current-temperature ratio varies according to the device temperature range:
For the range 0°C + 240°C the ratio is: I
out
= (T/15)+4 (T=temperature in °C)
For the range -40°C + 200°C the ratio is: I
out
= (T/15)+6.7 (T=temperature in °C)
Example: range 0°C + 240°C:
If T=100°C I
out
= 100/15+4= 10.67 mA (±0.2 mA)
Note: We recommend you use a screened and twisted cable; connect the twisted pair taking polarities into account and
lay the network avoiding narrow bends or ring windings. Always position the twisted pair far from power cables.
The NT538 AD has n.o selection (contact open ) / n.c (normally closed contact) for alarm and trip relays, programming
steps 26 to 29 page 15. The selection of the setting YES/NO introduces functions Fail Safe and No Fail Safe.
Setting YES (No Fail safe) normally open contacts are in positions 5-7 and 8-10 Alarm Trip, they switch only when
limits are reached preset temperature.
By setting NO (Fail Safe) normally closed contacts are in positions 5-7 and 8-10 Alarm Trip, they switch only when
limits are reached preset temperature.
NOTE: When the unit is located in one of the methods described below does not monitor heat, also the relay will all be
banned:
• Vis. display programming.
• PRG programming.
• Test of the relays.
The FAIL SAFE is temporarily disabled The ALARM and TRIP relays switch.
FAIL SAFE FUNCTION
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