Calculate the voltage drops in this loop-powered 4-20 mA transmitter circuit for the current conditions 4mA, 8mA, 12mA, 20mA.
Calculate the voltage drop at different points in the above circuit, like VCD, VEF, VFG, VAB at different loop currents (4mA, 8mA, 12mA, and 20mA)
In order for a loop-powered transmitter such as this to function adequately, there must be a minimum DC voltage between its terminals (VAB) at all times.
A typical value for this voltage is 12 volts (be aware that this minimum voltage level varies considerably between different manufacturers and models!). Identify what loop condition(s) may jeopardize this minimum supply voltage value, and how you as a technician would ensure the transmitter always received enough voltage to function.
The Rosemount 3144 temperature transmitter, for example, requires a minimum of 12 volts at its terminals to function in the analog mode, and 18.1 volts in order to properly function while communicating using the HART digital-over-analog protocol.
Note how the operation of such a 3144 transmitter in a loop with a 24 volt power supply and 300 ohms worth of resistance would be jeopardized near the upper end of the signal range.
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Credits: Tony R. Kuphaldt
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1- increase .
2- I am not sure and i hope to known the reason for that , I think we used multiple resistances to compare the value of volts for each resistance the insurance that is no deviation or drop of voltage .
3-we can used multimeter to read values for each segment between nodes and used Kirchhoff voltage law then compare the results with state of level transmitter.
What about the internal resistance of the transmitter? why it is not taken into account ?