The A421 Controls require an A99 sensor, and each A421 Control includes an A99 sensor. Any A99 Series sensor works with the A421 Series Controls. Do not replace an A99 Series sensor with any other brand, series, or type of temperature sensor. See Ordering information for available A99 Series sensor models.
You can extend the sensor leads in the field. See Table 1 for wire sizes and lengths. On long sensor cable runs, use shielded cable to reduce electromagnetic interference (EMI). Observe EMI best practices when you route sensor leads.
Do not completely immerse the A99 Series sensors in water or any other liquid. The A99 sensors are moisture tolerant and splash resistant but if you immerse the sensor, liquid can enter the sensor probe where the steel tube meets the wire cable and result in sensor failure, which voids any warranty.
In applications where the sensor may be exposed to a lot of moisture, splashing, or rain, it is best practice to mount the sensor in a vertical position with the cable at the bottom routed downward so that moisture can drain away from the steel probe. Use a suitable bulb well for complete fluid immersion applications. See Ordering information for information about bulb wells.
The A99 Series sensors are positive temperature coefficient (PTC) sensors. To test an A99 sensor, disconnect the sensor from the control and measure the resistance between the sensor leads in the following situations:
- When the temperature at the sensor is 77°F (25°C), the resistance should be 1,035 ohms.
- When the temperature at the sensor is 32°F (0°C), the resistance should be 855 ohms.
See Troubleshooting for more information.
When you connect an A99 sensor to a standard A421 Control, the control restricts the range of usable values from -40°F to 212°F (-40°C to 100°C).