20 OI/TTH300-EN Rev. D |
TTH300
7.4
Power supply
Two-wire technology, polarity safe; power supply lines = signal
lines
NOTICE
Following calculations apply for standard applications. This
should be taken into consideration when working with the
higher maximum current.
7.4.1
Power supply - HART
Input terminal voltage
— Non-Ex application:
U
S
= 11 ... 42 V DC
— Ex applications:
U
S
= 11 ... 30 V DC
Max. permissible residual ripple for input terminal voltage
— During communication in accordance with HART FSK
"Physical Layer" specification.
Undervoltage detection on the transmitter
— If the terminal voltage on the transmitter falls below a
value of 10 V, this may lead to an output current of I
a
≤
3.6 mA.
Maximum load
— R
B
= (supply voltage – 11 V) / 0.022 A
Fig. 16: Maximum load depending on input terminal voltage
A
TTH300
B
TTH300 In ia hazardous area design
C
HART
communication resistance
Maximum power consumption
— P = U
s
x 0.022 A
— e. g. 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.
Fig. 17
A
Transmitter
B
Supply isolator / PCS input with supply /
Segment coupler
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 ... 20 mA functionality
When connecting these components, observe the following
condition:
U
1min
≤ U
2min
- 22 mA x R
Standard application with HART functionality
By adding the resistance R
250
, the minimum input terminal
voltage U
2min
: U
1min
≤ U
2min
- 22 mA x (R + R
250
) can be
increased.
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 or without earthing. When
establishing a ground connection (minus side), make sure that
only one side of the terminal is connected to the equipotential
bonding.
Unless the profile HART protocol Rev. 7 is exclusively selected
during the ordering process, the device normally supports the
profile HART HART protocol Rev. 5 in the delivery
status. Subsequently user can change over to the profile
HART HART protocol Rev. 7 over a miniature switch. See
chapter for more details "Hardware settings" on page 22.
A11122
A
B
+
-
U
1
+
U
2
-
R
R
250
