Oil Temperature Indicators

Oil Temp Indicators 3

Microswitches Making and Breaking Capacity

Microswitches Making and Breaking Capacity

 Standard MicroswitchesHigh-Performance Microswitches
VoltageResistive LoadInductive LoadResistive LoadInductive Load
125 VAC5 A5 A10 A10 A
250 VAC5 A5 A10 A10 A
30 VDC5 A3 A10 A10 A
50 VDC1 A1 A3 A2,5 A
75 VDC0,75 A0,25 A1 A0,5 A
125 VDC0,5 A0,1 A0,5 A0,1 A
250 VDC0,25 A0,1 A0,25 A0,1 A


Description and General Specifications

These instruments are designed to measure the temperature of the insulating oil inside power transformer tanks. The oil temperature indicators can be fitted with one or two change-over microswitches suitable to control cooling equipments and / or protection circuits (alarm and trip) of the transformer.

Temperature sensing system : expansion type compensated for ambient temperature changes by means of a built-in compensating device.

Capillary tube protection :

  • copper tubing
  • flex galvanised steel + PVC armouring
  • flexible AISI 304 stainless steel armouring

Bulb : bronze or stainless steel.

Casing : aluminium alloy powder painted (RAL 7035) suitable to withstand to any climate and to heavy polluted atmosphere in as well tropical or arctic climates (-40 / +70°C). All components are made of corrosion resistant or surface treated ma- terials. The case is provided with a breather de- vice to avoid dew on the lens. To make cable lay- out quick and easy, the case is equipped with a large junction box that is completely separate from instrumentís sensing system.

Mechanical protection degree : IP 65.

Lens : special glass or polycarbonate.

Locking ring : nickel plated brass, transparent coated.

Standard measuring ranges :


⇒          0/+120°C
⇒        0 / +150°C
⇒        0/+200°C ̄

⇒    -20/+130°C
⇒       0/+150°C
⇒    -20/+140°C
⇒       0/+160°C
⇒       0/+200°C.

Measuring tolerance : 1,5% of full scale value.

Commutation tolerance : 2% of full scale value.

Commutation differential : 4% of full scale value. On customerís request the differential can be increased.

Insulation : 2000V 50Hz between terminals and earth for a 60 seconds time.


Max. temperature pointer : a red pointer, with reset knob located on the lens, indicates the max. tempera- ture measured by the instrument.

Operating Instructions and Maintenance

Mounting : mount the instrument on its machine or plant.

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

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

that allow the operator to choose the desired cable layout.

Setting : To set microswitches remove the locking ring and the glass or polycarbonate lens, stop the mi- croswitches setting dial with two fingers and slide the frictioned microswitches setting the pointers until they are located at the desired temperature. Replace the lens taking care that the max. temperature indicating pointer is located on the right side of the temperature indicating pointer. Lock the window, screwing the locking ring.

Maintenance : No particular maintenance is required. Only, on regular basis, schedule inspections to verify correct function and calibration. Typically a check of the precision must be done after 24 month and the check for contact functionality must be done at least once a year. In case the lens is dirty, clean it with a soft cloth, water and soap.

Finished Product Quality Control Tests

Instrument calibration : carried out through thermostatic baths controlled by a computer system. The procedure varies according to instruments scale. Example of procedure for a thermometer scale -20 / +130°C : the calibration 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 = 125°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 instrumentís bulb 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.