How does a ratiometer-type oil temperature gauge measure the temperature?

How does a ratiometer-type oil temperature gauge measure the temperature?

• A. A ratiometer measures the resistance of the temperature bulb. The indicator is calibrated in degrees Fahrenheit or Celsius rather than in ohms.
• B. It measures current through a thermistor
• C. It uses a Bourdon tube
• D. It uses an optical sensor

Answer: (A)

A ratiometer-type oil temperature gauge uses the sensing bulb as a resistance that changes with temperature and places it in a bridge circuit. As the oil temperature rises, the bulb’s resistance increases, altering the ratio between that resistance and a fixed reference in the bridge. The meter responds to this resistance ratio, and the pointer is calibrated so its position corresponds to a temperature value (degrees Fahrenheit or Celsius), not to an ohmic reading. This means the instrument translates a changing resistance into a temperature reading directly. The other options don’t fit because a ratiometer isn’t based on measuring current through a thermistor, using a Bourdon tube, or employing an optical sensor.

A ratiometer-type oil temperature gauge uses the sensing bulb as a resistance that changes with temperature and places it in a bridge circuit. As the oil temperature rises, the bulb’s resistance increases, altering the ratio between that resistance and a fixed reference in the bridge. The meter responds to this resistance ratio, and the pointer is calibrated so its position corresponds to a temperature value (degrees Fahrenheit or Celsius), not to an ohmic reading. This means the instrument translates a changing resistance into a temperature reading directly. The other options don’t fit because a ratiometer isn’t based on measuring current through a thermistor, using a Bourdon tube, or employing an optical sensor.