Emerson Rosemount 848T Reference Manual page 31

Reference Manual
00809-0100-4848
Figure 3-6: 848T Wireless Terminal Diagram
A
B
C
Note
For a device to be Intrinsically Safe, it must operate on only one power source. By
converting a 4–20 mA signal to a measurable millivolt signal, it is considered as a second
power source in the terminal block of the 848T, and voids the Intrinsically Safe approval.
This does not affect the division 2, non-incendive approvals so this configuration can still
be installed and operated in division 2 areas. Also, this technique should not be applied to
a 4–20 mA device currently connected to a loop control.
The mA signal should not be directly applied to the transmitter's millivolt terminals. Doing
this without the resistor may damage the electronics. The voltage applied across the
terminals should not exceed 1000 mV. Excessive voltage could damage the transmitter.
Using the Field Communicator or AMS, reconfigure the 848T sensor type to either 4–20
mA (Rosemount), 4–20 mA (NAMUR), 100 mV, or 1000mV. Note that when measuring
voltages less than 100mV, the 100mV sensor type should be selected for best accuracy.
The engineering units are user-selectable and can be either mA or mV.
the saturation and alarm thresholds for 4–20 mA (Rosemount) sensor type and
shows the saturation and alarm thresholds for 4–20 mA (NAMUR) sensor type.
Table 3-2: 4–20 mA (Rosemount) Saturation and Alarm
Transmitter status
Sensor Saturation
Sensor Out of Limits
Good
Sensor Out of Limits
Sensor Saturation
Emerson.com/Rosemount
A
-
+
C
+
-
B
4–20 mA device
Power supply
5 ohm
Analog input (mA)
> 21.71
20.8–21.71
3.9–20.8
3.79–3.9
< 3.79
Table 3-2
Measured voltage (mV)
> 108.55
104–108.55
19.5–104
18.95–19.5
< 18.95
Installation
September 2019
shows
Table 3-3
Analog region
Upper Alarm
Upper Saturation
Normal Region
Lower Saturation
Lower Alarm
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