Johnson Controls ST-D24 Thermistor

The Johnson Controls ST-D24 is a precision 10k ohm Type II thermistor engineered for accurate air temperature monitoring within commercial HVAC ductwork. Featuring an 8-inch stainless steel probe, this sensor ensures optimal immersion depth to mitigate wall-effect errors and provide reliable feedback to building automation systems (BAS). With an operating temperature range spanning from -40?F to 221?F (-40?C to 105?C), the ST-D24 is designed for high-demand environments, maintaining structural integrity against moisture and vibration. This duct mount temperature sensor is a standard replacement for Metasys systems and other controllers requiring a 10k ohm NTC curve. The robust stainless steel probe construction prevents corrosion in high-humidity return air streams, while the integrated junction box simplifies field wiring for contractors. Whether utilized for discharge air sensing or economizer control, the ST-D24 thermistor ensures tighter setpoint control and improved system efficiency across various air handling unit (AHU) configurations.

• Wide Operating Envelope: Capable of monitoring extreme conditions from -40?F to 221?F without signal degradation.
• Durable Probe Design: 8-inch stainless steel probe provides high thermal conductivity and resists mechanical wear.
• NTC 10K Ohm Type II Curve: Native compatibility with Johnson Controls Metasys and various third-party DDC controllers.
• Simplified Installation: Standard duct flange and terminal block design reduce labor time during retrofit or new construction.

Common Technical Inquiries

How do I verify the resistance of the ST-D24 during troubleshooting?
Disconnect the sensor from the controller and measure the resistance across the leads using a multimeter set to ohms. At 77?F (25?C), the Johnson Controls ST-D24 should read exactly 10,000 ohms. A significant deviation indicates a potential short or sensor drift.

Is this sensor compatible with non-Johnson Controls systems?
Yes, as long as the controller is configured to accept a 10k ohm Type II NTC thermistor curve. It is a common standard for many global BAS platforms.

Can the 8-inch probe be shortened for smaller branch ducts?
The stainless steel probe is a sealed unit containing the thermistor bead at the tip; it cannot be cut or shortened without destroying the internal sensing element and vacuum seal.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.