For veteran technicians servicing indirect-fired make-up air units, the Maxitrol TS121 discharge air temperature sensor is the critical component for maintaining a stable 55-90°F terminal temperature range. Specifically engineered for integration with Selectra Series 20, 21, 30, and 31 modulation systems, this thermistor-based sensor delivers a resistance of 4,500 ohms at 77°F, providing the Maxitrol amplifier with the sub-second response times required to adjust Maxitrol modulator-regulator valves. Unlike mechanical butterfly valves or mod motors, the TS121 facilitates a continuous, linear gas flow adjustment to counteract rapid fluctuations in inlet air temperature. When installed within a compatible mixing tube, the TS121 ensures the discharge airstream stays within the operator's set point, preventing energy waste and equipment cycling. This sensor is functionally matched with the TD121 remote temperature selector; for proper system operation, ensure both components share the same 55-90°F calibration. For troubleshooting, a 4,500-ohm test resistor can be used at the amplifier terminals to verify electronic modulation functionality. This industrial HVAC sensor is built to withstand the high-velocity discharge environments of heavy-duty atmospheric burners and rooftop units. Key Benefits Precise Modulation: Provides a 42-ohm resistance change per degree to the Series 21 amplifier for precise flame control. System Compatibility: Seamlessly integrates with Maxitrol MT1 mixing tubes and Selectra Series 20/30/21/31 gas modulation systems. Enhanced Efficiency: Eliminates the "hunting" common in mechanical dampers by providing instantaneous feedback to the MR valve. Heavy-Duty Reliability: Designed specifically for make-up air heating and indirect-fired industrial units. Common Questions Which mixing tube is required for the TS121? The TS121 must be installed in a mixing tube (such as the MT1-9 or MT1-12) to protect the sensing element from thermal radiation and to ensure it measures a representative sample of the discharge air. Can I use a TS121A in place of a TS121? No. The TS121 is calibrated for 55-90°F, while the TS121A is rated for 80-130°F. The sensor range must match the amplifier and remote selector range for the system to modulate correctly. How do I test if my TS121 sensor is faulty? Check the resistance across the sensor leads. At 77°F, you should read approximately 4,500 ohms. An open circuit or a reading significantly above 12,000 ohms typically indicates a failed sensor or wiring issue. 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.
