Prothermo NMT 538
18
Hauser Systems & Gauging
3.4
HART line cabling
NMT538 is a HART slave instrument. that requires power supply for the device operation and
communication signal on the same 2 cables.
Figure 7:NMT 538 terminal board
Required DC voltage for NMT538 operation is minimum 16 to maximum 30 volt.
With the connection to the Proservo NMS53x, normally supply DC24V ±10% to the NMT538. The
Tank side monitor NRF590 can normally supply DC16±1V on the IS HART loop.
Both the NMT538 and host instrument recognizes 0.5mA current shift as the trigger of data
transmission. I.e, NMT538 normally consumes 9.0mA at temperature measurement only. The
current consumption decreases to approximately 8.5mA while NMT538 is receiving command
from the host gauge on the HART line. On the other hand, the current consumption increases to
approximately 9.5mA while NMT538 is sending data to the host gauge as a response to the
previous command.
Warning!
Before opening the cover of the Prothermo NMT538 for maintenance, switch off the power supply
of the Proservo NMS53x or the Tank side monitor NRF590. Either of these 2 instruments normally
are the host gauge to supply DC voltage on the IS HART line to the NMT538.
3.4.1
Protection from line noise
The following precautions are required to rule out any malfunction by line noise.
-The minimum conductor size for the HART transmission distance up to 1500m should be used
0.51mm diameter (#24 AWG) shield twisted pair cable and 0.81mm diameter (#20AWG) for longer
distance.
-Use appropriate cable size reference to the conditions described below chart 1.
Grounding for cable screen
Screened twisted pair
or steel armored wire
Temp.HART
from NMT 538
+ terminal 1
- terminal 2
to NRF 590
+ terminal 24 or 26
- terminal 25 or 27
to NMS53...
+ terminal 24
- terminal 25
Cable gland
(Refer to specifications)
Temp. RTD signal (max. 16 points)
- Whessoe Varec 1700
- Whessoe Varec 9909
- Weed Beacon MW & MWR
FG
1 2
Screen
3 Installation
