Power Supply - Emerson Rosemount 248 Reference Manual

Section 2: Installation
March 2014
Lead wire imbalance seen by the transmitter = 0.5 

Error due to amb. temp. variation
Lead wire resistance seen by the transmitter = 150 m × 2 wires × 0.025  /m = 7.5 
2.7

Power supply

To communicate with a transmitter, an 18.1 Vdc minimum power supply is required. The power
supplied to the transmitter should not drop below the transmitter lift-off voltage (see
Figure
configured, the transmitter may interpret the configuration information incorrectly.
The dc power supply should provide power with less than 2 percent ripple. The total resistance
load is the sum of the resistance of the signal leads and the load resistance of any controller,
indicator, or related pieces of equipment in the loop. Note that the resistance of intrinsic safety
barriers, if used, must be included.
Figure 2-8. Load Limits
Maximum load = 40.8 x (Supply voltage – 12.0)
18
--------------------------------------------------------------------------------- -
=
Basic error
 0.00385  /  C
Error due to amb. temp. var. of
 0.0039  /  C
------------------------------------------------------------------------------------------------------ -
=
 0.00385  /  C
Pt100 2-wire RTD:
Lead Wire Resistance
--------------------------------------------------------- -
=
Basic Error
--------------------------------------------------------------------------------- -
=
Basic error
 0.00385  /  C
Error due to amb. temp. var. of
 0.0039  /  C    25 C
------------------------------------------------------------------------------------------------------ -
=
 0.00385  /  C  
2-8). If the power drops below the lift-off voltage while the transmitter is being
4–20 mA dc
1322
1100
1000
750
500
Operating
250
region
0
10 20 30 40 42.4
12.0
Supply voltage (V dc)
0.5 
1.3 C
=
   100  

25 °C
   25 C    0.5  

=
0.13
   
100
   
R
Pt o
     T   
Lead Wire Resistance
Cu amb
---------------------------------------------------------------------------------------------------------------- -
=
    
R
Pt
7.5 
19.5 C
=
   100  

25 °C
   7.5  
 1.9 C
=
 
100
Reference Manual
00809-0100-4825, Rev CB
·
C


o
Installation