Microswitches Equipped Thermometers

Microswitches 1

Description and General Specifications

This instrument is designed to measure and control the temperature in oil filled distribution transformers and is made for outdoor mounting in as well tropical or arctic climates (ambient temperature range -40°C / +70°C). All components are made of corrosion resistant or surface treated materials. This thermometer is fitted with 1 or 2 change-over (SPDT) microswitches working both normally open and normally closed (three terminals each microswitch) and is supplied with a junction board with 3 or 6 terminals 2 + earth. Max. cable section = 2,5mm

Temperature sensing system : expansion type (liquid filled system), compensated for ambient temperature changing by means of a bimetallic spring.
Casing : aluminium alloy with powder painting high protection degree. On request case can be provided with an air breather device for ventilation.
Mechanical protection degree : IP 65.
Measuring range : -20 / + 120°C
Switches making and breaking capacity (non inductive) : 5A 250V AC 250mA 250V DC 500mA 125V DC
Insulation test : 2000V 50Hz between terminals and earth for a 60 seconds time.
Measuring tolerance : 1,5% of full scale value.
Commutation tolerance : 2% of full scale value

Operating Instructions and Maintenance

Mounting : mount the instrument on its machine or plant by putting the thermometer bulb into the thermometer pocket on the transformer cover and by screwing the thermometer connection.

Attention : the connection must be locked by using a spanner. Trying to lock the connection by rotating thermometer’s head may damage the instrument. Before locking the thermometer take care that its dial is oriented to consent a perfect readability.

Contact setting : remove the thermometer cover by unscrewing the 4 stainless steel screws. Rotate the knob of each contact till the small pointer is located at the desired set point temperature Re-position the cover taking care that the sealing gasket is correctly located into its seat ant that the max temperature pointer (if any) is on the right side of the indicating pointer. Screw the stainless steel screws.

Cable layout : the numerations 1-2 indicate the microswitches progression. Close to the terminals you will find the following abbreviations :

  • C = common
  • NO = normally open
  • NC = normally closed

that allow the operator to choose the desired cable layout. When connecting the microswitches terminals don’t forget to connect the earth terminal too.

No particular maintenance is required. Only periodical inspections ( typical interval 12 months ) to verify pre- cision, functions and electrical connections. When the instrument is equipped with polycarbonate lens, cleaning must be done with care in order to avoid scraps on the surface. Use water and soap only.

Finished Product Quality Control Tests

Instrument calibration : carried out through thermostatic baths controlled by a computer system. The procedure varies according to instruments scale. The calibration procedure, being the thermometer scale -20 / +120°C is made using 5 different baths set at the following temperatures :

  • bath 1 = -20°C
  • bath 2 = 20°C
  • bath 3 = 50°C
  • bath 4 = 100°C
  • bath 5 = 115°C

Calibration procedure :

Step 1: a check is carried out to see whether the temperature taken by the instrument under test differs from that taken through the sample sensor by more than the 70% of the maximum allowed instrument reading tolerance value. This test is performed by sequentially plunging the TEMPERATURE INDICATOR bulb into successive temperature increasing thermostatic baths : -20°C / +20°C / +50°C / +100°C / +125°C.

Step 2: the instrument is heated until the instrument pointer exceeds by 20% the angular full scale value.

Step 3: step 1 is repeated, but inversely.

Microswitches actuation test : performed through a computer controlled testing unit . The bulb is immersed in a thermostatic bath. The computer changes the temperature inside of the bath and by means of suitable sensors verifies the commutation tolerance, the commutation differential, the electrical circuits of each microswitch. At the end of the test a report is directly printed by the computer.

Check of instrument mechanical protection degree : IP 65.

Insulation test : carried out by means of a microprocessor controlled testing unit.

Note : all the collected data are immediately transferred, by means of the computer net, to the quality control and to the design departments to be supervised and evaluated. In our files, we keep all the above mentioned informations and we can supply to the customer detailed reports regarding the performances of each instrument delivered.