Rosemount 248, Reference Manual

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Reference Manual
00809-0100-4825, Rev BB
August 2005
Rosemount 248
2-12
Figure 2-8. Load Limits
Surges/Transients
The transmitter will withstand electrical transients of the energy level
encountered in static discharges or induced switching transients. However,
high-energy transients, such as those induced in wiring from nearby lightning
strikes, welding, heavy electrical equipment, or switching gears, can damage
both the transmitter and the sensor. To protect against high-energy transients,
install the transmitter into a suitable connection head with the Rosemount 470
Transient Protector. Refer to the Rosemount 470 Transient Protector Product
Data Sheet (document number 00813-0100-4191) for more information.
Ground the Transmitter
The transmitter will operate with the current signal loop either floating or
grounded. However, the extra noise in floating systems affects many types of
readout devices. If the signal appears noisy or erratic, grounding the current
signal loop at a single point may solve the problem. The best place to ground
the loop is at the negative terminal of the power supply. Do not ground the
current signal loop at more than one point.
The transmitter is electrically isolated to 500 V ac rms (707 V dc), so the input
circuit may also be grounded at any single point. When using a grounded
thermocouple, the grounded junction serves as this point.
NOTE
Do not ground the signal wire at both ends.
Ungrounded Thermocouple, mV, and RTD/Ohm Inputs
Each process installation has different requirements for grounding. Use the
grounding options recommended by the facility for the specific sensor type, or
begin with grounding Option 1 (the most common).
4–20 mA dc
1322
1100
1000
750
500
250
0
10
12.0
20 30 40 42.4
Lo
ad
(
O
h
m
s)
Supply Voltage (V dc)
Operating
Region
6
44_08A
Maximum Load = 40.8 x (Supply Voltage – 12.0)