htk4014a600p_04
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loop current, mA
vo
lta
ge,
V
0
2
4
6
8
10
12
14
16
18
20
22
8
9
10
11
12
13
14
15
16
17
18
19
20
voltage drop
over 250
resistance at
4 mA
Ω
minimum input voltage V
(measured at MicroTREK terminals)
input
voltage drop
over 250
resistance at
20 mA
Ω
minimum
y
,V , , for a loop
resistance, R of
(measured at
the terminals of the power supply)
suppl voltage
supply
loo p
250
Ω
Line A = minimum voltage at the MicroTREK 2-wire terminals
Line B = minimum supply voltage (for voltage drop caused by a 250
Ω
loop resistance)
Example for calculating the power supply: The voltage drop is tested at 22 mA:
U
power minimum 22
= 22 mA x load imp U
input minimum 22
U
power minimum 22
= 22 mA x 250
Ω
+ 10 V = 5.5 V + 10 V = 15.5 V
In order to cover the whole current range, the voltage drop must also be tested at 4 mA:
By analogy, the following applies:
U
power minimum 4
= 4 mA x load imp U
input minimum 4
U
power minimum 4
= 4 mA x 250
Ω
+ 18 V = 1 V + 18 V = 19 V
At a load impedance of 250
Ω
a power supply voltage of 19 V is sufficient to energize the current device range of 4 – 20 mA.