LM135, LM135A, LM235, LM235A, LM335, LM335A

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SNIS160E – MAY 1999 – REVISED FEBRUARY 2015

10.3 Waterproofing Sensors

Meltable inner-core, heat-shrinkable tubing, such as manufactured by Raychem, can be used to make low-cost

waterproof sensors. The LM335 is inserted into the tubing about 0.5 inches from the end and the tubing heated

above the melting point of the core. The unfilled 0.5-inch end melts and provides a seal over the device.

10.4 Mounting the Sensor at the End of a Cable

The main error due to a long wire is caused by the voltage drop across that wire caused by the reverse current

biasing the LM135 on. Table 2 shows the wire AWG and the length of wire that would cause 1°C error.

Figure 34. Cable Connected Temperature Sensor

Table 2. Wire Length for 1°C Error Due to Wire Drop

IR = 1 mA

IR = 0.5 mA

(1)

AWG

FEET

FEET

14

4000

8000

16

2500

5000

18

1600

3200

20

1000

2000

22

625

1250

24

400

800

(1)

For IR = 0.5 mA, the trim pot must be deleted.

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