Reference Manual
00809-0100-4728, Rev HA
December 2002
Models 644H and 644R
2-12
Lead wire imbalance seen by the transmitter = 0.5
Ω
• Pt100 2-wire RTD:
Lead wire resistance seen by the transmitter = 150 m × 2 wires ×
0.025
Ω
/m = 7.5
Ω
POWER SUPPLY
To communicate with a transmitter, a 18.1 V dc minimum power supply is
required. The power supplied to the transmitter should not drop below the
transmitter lift-off voltage (see Figure 2-9). If the power drops below the lift-off
voltage while the transmitter is being 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 2-9. Load Limits
Basic error
0.5
Ω
0.00385
Ω
/
Ω
°
C
(
)
100
Ω
(
)
×
---------------------------------------------------------------------------------
1.3
°
C
=
=
Error due to amb. temp. var. of 25 °C
±
0.0039
Ω
/
Ω
°
C
(
)
25
°
C
(
)
×
0.5
Ω
(
)
×
0.00385
Ω
/
Ω
°
C
(
)
100
Ω
(
)
×
---------------------------------------------------------------------------------------------------------
13
·
°
C
±
=
=
Basic Error
Lead Wire Resistance
α
Pt
R
o
×
(
)
----------------------------------------------------------
=
Error due to amb. temp. variation
α
Cu
(
)
∆
T
amb
(
)
×
Lead Wire Resistance
(
)
×
α
Pt
(
)
R
o
(
)
×
-------------------------------------------------------------------------------------------------------------------
=
Basic error
7.5
Ω
0.00385
Ω
/
Ω
°
C
(
)
100
Ω
(
)
×
---------------------------------------------------------------------------------
19.5
°
C
=
=
Error due to amb. temp. var. of 25 °C
±
0.0039
Ω
/
Ω
°
C
(
)
25
°
C
(
)
×
7.5
Ω
(
)
×
0.00385
Ω
/
Ω
°
C
(
)
100
Ω
(
)
×
---------------------------------------------------------------------------------------------------------
1.9
°
C
±
=
=
Maximum Load = 40.8 x (Supply Voltage – 12.0)
4–20 mA dc
1322
1100
1000
750
500
250
0
1012.0 20
30
40 42.4
L
o
ad
(Ohm
s)
Supply Voltage (V dc)
Operating
Region
644_0
8A
Summary of Contents for Rosemount 644h
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Page 4: ......
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Page 50: ...Reference Manual 00809 0100 4728 Rev HA December 2002 Models 644H and 644R 4 10 ...
Page 64: ...Reference Manual 00809 0100 4728 Rev HA December 2002 Models 644H and 644R A 14 ...
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