A 4-20mA loop is wired in series through a transmitter, a PLC input card (250 ohm resistor), and a chart recorder (250 ohm resistor). The power supply is 24VDC. The transmitter requires a minimum of 12VDC to operate. Will this loop function at 20mA?
Answers
ANo. The resistance is too high and will choke the current to 10mA
BYes, but the chart recorder will not read accurately
CYes. The voltage drop across the resistors is 10V (500 ohms * 0.02A), leaving 14V for the transmitter
DNo. The transmitter will receive 24V and burn out
Correct answer: C — Yes. The voltage drop across the resistors is 10V (500 ohms * 0.02A), leaving 14V for the transmitter
Total resistance = 500 ohms. At 20mA (0.02A), V_drop = I*R = 0.02 * 500 = 10V. 24V - 10V = 14V remaining at the transmitter. Since 14V > 12V minimum, the loop functions perfectly.
MIFOTRA exam practicealigned to CompTIA (General IT) / BICSI·4 marks·Hard