2-3
Installation
GENERAL
CONSIDERATIONS
Electrical temperature sensors such as resistance temperature
detectors (RTDs) and thermocouples (T/Cs) produce low-level signals
proportional to temperature. The Model 3144 and 3244MV transmitters
convert low-level sensor signals to a standard 4–20 mA dc signal that is
relatively insensitive to lead length and electrical noise. This current
signal is then transmitted to the control room via two wires.
Figures 2-9 and 2-12 show recommended mounting configurations for
transmitters and sensor assemblies. Refer to Section 6: Options for
additional transmitter mounting accessories.
ELECTRICAL
CONSIDERATIONS
Proper electrical installation is necessary to prevent errors due to
sensor lead resistance and electrical noise. Shielded cable should be
used for best results in electrically noisy environments. The current
loop must have between 250 and 1100 ohms in order to communicate
with a HART communicator. Refer to Figure 2-4 on page 2-5 for sensor
and current loop connections.
Power Supply
To communicate with a transmitter, you will need a 17.75 V dc
minimum power supply. The power supplied to the transmitter should
not drop below the transmitter lift-off voltage (see Figure 2-2). 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% 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 piece of
equipment in the loop. Note that the resistance of intrinsic safety
barriers, if used, must be included.
NOTE
Do not allow the voltage to drop below 12.0 V dc at the transmitter
terminals when changing transmitter configuration parameters, or
permanent damage to the transmitter could result.
Figure 2-2. Load Limits.
1322
1000
750
250
0
10
12.0
20
30
40 42.4
Supply Voltage (V dc)
Maximum Load = 43.5
3
(Supply Voltage – 12.0)
Operating
Region
4–20 mA dc
Loa
d
(O
h
ms
)
500
1100