Robertshaw DMS T99 Sensor Integration with MNL Controller Using Curve Fit Object

[Product_Support]

Issue

Can the Robertshaw DMS T99 sensor be connected to an MNL controller using the Curve Fit object?

Product Line

TAC IA Series

Environment

• Robertshaw DMS T99
• MNL controller

Cause

The site requires the use of a Robertshaw DMS T99 sensor with an MNL controller, but the sensor’s characteristics differ from standard Balco sensors.

Resolution

The T99 sensor is a 2000 Ω silicon-based RTD with linearity similar to Balco. To integrate it with an MNL controller:

1. Wiring:

   • Connect the T99 sensor to the MNL controller’s UI input.
   • Add a parallel 2000 Ω ±1% shunt resistor.

2. AI Object Configuration:

   • Select Balco type in the AI object.

3. Curve Fit Adjustment:

   • Use a Curve Fit object to correct temperature readings.
   • Configure X and Y data points as follows:
     • X (Balco temperatures): 52.5, 61.6, 70.0, 78.4, 86.6, 94.8
     • Y (Corrected T99 temperatures): 32.0, 50.0, 68.0, 86.0, 104.0, 122.0

Note: The A/D degree per count resolution is approximately 0.15°F per count, which is twice that of Balco.