[FAQ] Remote Temperature Sensors —How far can my remote be from the remote temperature sensor?

While there is no absolute limit on how far the remote junction can be from the temperature sensor there are factors that will indirectly limit the distance. Parasitic capacitance would most likely be the first limiting factor. Most our device cannot handle more than 1000 pF without causing noticeable temperature errors. However, system level parasitics such as inductive/capacitive noise and series resistance need to be minimized and stay within datasheet limits to achieve accurate temperature.  

Layout must adhere to the following guidelines:

1. Place the remote temperature sensor as close to the remote junction sensor as possible.
2. Route the D+ and D– traces next to each other and shield them from adjacent signals through the use of ground guard traces, as shown in the below figure. If a multi-layer PCB is used, bury these traces between the ground or V+ planes to shield them from extrinsic noise sources. 5-mil (0.127 mm) PCB traces are recommended.

3. Minimize additional thermocouple junctions caused by copper-to-solder connections. If these junctions are used, make the same number and approximate locations of copper-to-solder connections in both the D+ and D– connections to cancel any thermocouple effects.

4. Use a 0.1-μF local bypass capacitor directly between the V+ and GND of the remote temperature sensor. For optimum measurement performance, minimize filter capacitance between D+ and D– to 1000 pF or less. This capacitance includes any cable capacitance between the remote temperature sensor and the remote temperature sensor device

5. If the connection between the remote temperature sensor and the remote temperature sensor is less than 8-in (20.32 cm) long, use a twisted-wire pair connection. For lengths greater than 8 in, use a twisted, shielded pair with the shield grounded as close to the remote temperature sensor as possible. Leave the remote sensor connection end of the shield wire open to avoid ground loops and 50/60-Hz pickup.

6. Thoroughly clean and remove all flux residue in and around the pins of the remote temperature sensor to avoid temperature offset readings as a result of leakage paths between D+ and GND, or between D+ and V+.