Point-To-Point Network - Siemens 7MF4033 series User Manual

Installation
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4.3.5.1 Point-to-Point Network

The graph in Section 4.3.5 defines an analog mode transmitter's operating region for the allowable ranges
of supply voltage and network resistance. Perform the following calculations to ensure that the power
supply output voltage permits the transmitter to remain within the indicated operating range.
1. Calculate the minimum power supply output voltage.
The minimum network power supply voltage requirement is a function of Network Resistance and
full scale current (20 mA), and is calculated by the following formula:
Minimum Power Supply Output Voltage = 10.5 volts + (0.02 × Network Resistance in ohms)
Power supply output voltage must be greater than the calculated value. The minimum voltage across
the input terminals of a transmitter is 10.5 volts.
2. Calculate the maximum power supply output voltage.
The maximum network power supply voltage is a function of Network Resistance and zero scale
current (4 mA), and is calculated by the following formula:
Maximum Power Supply Output Voltage = V
Power supply output voltage must be less than the calculated value. The maximum voltage (
permitted across the input terminals is:
•
Non-intrinsically safe transmitter: 45 volts
•
Intrinsically safe transmitter: 30 volts
4-16
Power Supply vs. Loop Resistance
15.5
15 20
FIGURE 4-10 Power Supply vs. Loop Resistance
+ (0.004 × Network Resistance in ohms)
max
24
30
25
Power Supply, Vdc
UMSITRPDS3-1
35 40
45
November 2005
V )
max