Functioning of the MAX temperature sensor
- NO: the electrical contact closes when the pre-set temperature is reached at 80°C.
- NC: the electrical contact opens when the pre-set temperature at 80°C is reached.
Electrical features | MAX temperature sensor |
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Power supply | AC/DC |
Electric contacts | NO normally open NC normally closed |
Voltage / Maximum current | 250 Vac - 2 A | (resistive loads) DIN 43650 C |
115 Vac - 3A |
24 Vdc - 3 A |
12 Vdc - 4 A |
30 Vac, 30 Vdc | KN |
Voltage range (Type KN) | <30 Vac, <30 Vdc |
Minimum current | 50 mA |
Cable gland | Pg 7 (for cables in sheath with Ø 6 or 7 mm) |
Conductors cross-section | Max. 1.5 mm2 |
Functioning of the temperature electrical probe (STL)
The working principle of the temperature probe is to measure the variation of resistance of a platinum element: 100 ohm = 0°C, 138.4 ohm = 100°C.
The function between temperature (T) and resistance (R) is approximately linear over a small temperature range: for example, if you assume that it is linear over the 0° to 100°C range, the error at 50°C is 0.4°C.
For precision measurement, it is necessary to linearise the resistance to give an accurate temperature. The most recent definition of the function between resistance and temperature is International Temperature Standard 90 (ITS-90). The function between resistance and temperature, obtained in laboratory tests, measuring directly the resistance value on the contacts is shown in the graph. We suggest, anyway, to set the system in order to compensate both heat dissipation and cable resistance.
The temperature variation of 1°C causes a 0.384 ohm variation in the probe resistance. Therefore, even a small error in the resistance measurement (for example, if the resistance of the cables connecting to the probe were not considered) translates into a significant error in the temperature measurement.
Because of the low signal levels, it is important to keep any cables away from electric cables, motors, switchgear and other devices that may emit magnetic or electrical noise. Using screened cable, with the screen grounded at one end, may help to reduce interference.
Furthermore, if long connection cables are used, make sure that the signal measurement and reception device is designed to compensate for the resistance of the cables themselves.
Electrical features | Temperature probe |
Power supply | AC/DC |
Maximum current | 1mA |
Cable gland | Pg 7 (for cables in sheath with Ø 6 or 7 mm) |
Conductors cross-section | Max. 1.5 mm2 |
Do not mount this indicator in proximity to magnetic fields. |