User's Manual

7ML19985JE03 SITRANS LR250 (HART) – INSTRUCTION MANUAL Page 141
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D: Technical Reference
Curve 2 (Flameproof, Increased Safety, Explosion-proof)
Loop Voltage versus Loop Resistance
Startup Behavior
Notes:
• SITRANS LR250 is designed to start reliably with a power supply capable of
delivering at least 25 mA.
• When connected to a power supply with a current limit of < 25 mA, the LR250 may
not start reliably.
Power Supply Requirements
0
50
100
150
200
250
300
350
400
15 20 25 30
Loop Voltage - V
L
(Source Voltage)
Loop Resistance - R
L
(30.0V, 375 ohms)
RL = 14.88 * VL - 71.43
(21.6V, 250 ohms)
(18.2V, 0 ohms)
RL = 73.53 * VL - 1338.24
Power Supply Requirements
Loop Voltage – V
L
Loop Resistance – R
L
ALLOWABLE
OPERATING AREA
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
Time (seconds)
Current (mA)
No Current Limit Current Lim ited Power Supply
Typical Startup Current
Time (seconds)
Current (mA)
Loop Power Supply
without Current Limit
Loop Power Supply with
25 mA Current Limit
Current-limited powerNo current limit