You are checking the supply chilled water temperature thermistor probe on a high-pressure hermetic centrifugal chiller. Using the illustrated chart, what statement is true if the supply water temperature is verified 45°F with a digital thermometer. See illustration GS-RA-48.
• Using the 45°F row on the thermistor temperature vs resistance/voltage chart • Difference between resistance (ohms) and voltage drop (volts) columns • Proper way to measure a thermistor’s resistance (power off and probe isolated from the circuit)
• On the 45°F line of the chart, which value is labeled as RESISTANCE (Ohms) and which is labeled as VOLTAGE DROP (V)? • If you try to measure resistance with the thermistor still connected to the control circuit, what other components could affect the reading? • Which answer choice correctly matches: (1) chart resistance value at 45°F and (2) the correct measurement condition for an ohmmeter?
• Verify that the number used from the chart comes from the RESISTANCE (Ohms) column, not the voltage column. • Confirm that the answer choice you pick says control power off when measuring resistance with an ohmmeter. • Confirm that the answer choice you pick says the thermistor probe is isolated (one lead lifted) so only the thermistor’s resistance is being measured.
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