ABB TTF200 - Power Supply and Voltage Drop Analysis

24 TTF200 FIELD-MOUNT TEMPERATURE TRANSMITTER | OI/TTF200-EN REV. B
… 7 Electrical connections
… Electrical data for inputs and outputs
Power supply
Two-wire technology, polarity safe; power supply lines = signal
lines
Note
Following calculations apply for standard applications. This
should be taken into consideration when working with a higher
maximum current.
Input terminal voltage
Non-Ex application:
U
S
= 11 to 42 V DC
Ex applications:
U
S
= 11 to 30 V DC
Maximum permissible residual ripple for input terminal
voltage
During communication, this is in accordance with the HART® FSK
‘Physical Layer’ specification.
Undervoltage detection on the transmitter
If the terminal voltage on the transmitter down-scales a value of
10 V, this may lead to an output current of I
a
≤ 3.6 mA.
Maximum load
R
B
= (U
S
− 11 V) / 0.022 A
A TTF200
B TTF200 in Ex-applications
C HART® communication resistance (R
B
)
Figure 22: Maximum load depending on input terminal voltage
Maximum power
• P = U
s
× 0.022 A
• Example: U
s
= 24 V  P
max
= 0.528 W
Voltage drop on the signal line
When connecting the devices, note the voltage drop on the
signal line. The minimum supply voltage on the transmitter must
not be undershot.
A11122
AB
+
-
U
1
+
U
2
-
R
R
250
A Transmitter B Supply isolator / DCS input with
supply / segment coupler
Figure 23: HART load resistance
U
1min
: Minimum supply voltage on the transmitter
U
2min
: Minimum supply voltage of the supply isolator /
DCS input
R: Line resistance between transmitter and supply isolator
R
250
: Resistance (250 Ω) for HART functionality
Standard application with 4 to 20 mA functionality
When connecting these components, observe the following
condition:
U
1min
≤ U
2min
- 22 mA × R
Standard application with HART functionality
Adding resistance R
250
increases the minimum supply voltage
U
2min
: U
1min
≤ U
2min
- 22 mA × (R + R
250
)
For HART functionality, use supply isolators or DCS input cards
with a HART mark. If this is not possible, a resistance of ≥ 250 Ω
(< 1100 Ω) must be added to the interconnection.
The signal line can be operated with / without grounding. When
establishing a ground connection (minus side), make sure that
only one side of the terminal is connected to the equipotential
bonding.