Abstract:
A thermocouple welding test apparatus for testing whether a thermocouple is normally welded includes a first comparison circuit, a second comparison circuit, a switch circuit and an indication circuit. The first comparison circuit receives a first DC voltage from the thermocouple, and compares the first DC voltage with a first reference voltage to output a first control signal. The second comparison circuit receives a second DC voltage from the thermocouple, and compares the second DC voltage with a second reference voltage to output a second control signal. The switch circuit receives the first control signal and the second control signal, and outputs an indication signal accordingly. The indication circuit receives the indication signal, and indicates whether the thermocouple is normally welded accordingly.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a thermocouple welding test apparatus for testing whether a thermocouple is normally welded. 
         [0003]    2. Description of Related Art 
         [0004]    A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used as a type of temperature sensor for measuring temperature, and can also convert heat signal into electric signal, such as voltage signal. Thermocouples for practical measurement of temperature are junctions of specific alloys which have a predictable and repeatable relationship between temperature and voltage. Different alloys are welded together by a special apparatus to form thermocouples. The thermocouples need to be tested for whether the alloys are normally welded together before use, for ensuring the precision of the measurement. 
         [0005]    Therefore there is a need for improvement in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Many aspects of the embodiments can be better understood with references to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0007]      FIG. 1  is a block diagram of an embodiment of a thermocouple welding test apparatus. 
           [0008]      FIG. 2  is a circuit diagram of the thermocouple welding test apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
         [0010]      FIG. 1 , illustrates a thermocouple welding test apparatus in accordance with an embodiment. The thermocouple welding test apparatus is adapted to test whether a thermocouple  500  is normally welded. The thermocouple welding test apparatus includes a first comparison circuit  100 , a second comparison circuit  200 , a switch circuit  300  and an indication circuit  400 . The first comparison circuit  100  is electrically connected to the thermocouple  500  to receive a first DC voltage. The first comparison circuit  100  is adapted to compare the first DC voltage with a first reference voltage to output a first control signal. The second comparison circuit  200  is electrically connected to the thermocouple  500  to receive a second DC voltage. The second comparison circuit  200  is adapted to compare the second DC voltage with a second reference voltage to output a second control signal. The switch circuit  300  is adapted to receive the first control signal and the second control signal, and output an indication signal accordingly. The indication circuit  400  is adapted to receive the indication signal, and indicate whether the thermocouple  500  is normally welded accordingly. 
         [0011]      FIG. 2 , illustrates the first comparison circuit  100  in accordance with one embodiment. The first comparison circuit  100  includes a first comparator U 1 , a first resistor R 1 , a second resistor R 2 , a third resistor R 3  and a fourth resistor R 4 . An inverting input terminal of the first comparator U 1  is electrically connected to a first terminal of the thermocouple  500  via the first resistor R 1 . The inverting input terminal of the first comparator U 1  is adapted to receive a third DC voltage via the second resistor R 2 . A non-inverting input terminal of the first comparator U 1  is electrically connected to the first terminal of the thermocouple  500  via the third resistor R 3 . The non-inverting input terminal of the first comparator U 1  is adapted to receive the third DC voltage via the fourth resistor R 4 . A connection point between the first terminal of the thermocouple  500 , the first resistor R 1  and the third resistor R 3  is grounded. A second terminal of the thermocouple  500  is electrically connected to a connection point between the first resistor R 1  and the second resistor R 2 . An output terminal of the first comparator U 1  is adapted to output the first control signal. In one embodiment, a resistance of the first resistor R 1  is greater than a resistance of the third resistor R 3 . Resistances of the first resistor R 1 , the second resistor R 2  and the fourth resistor R 4  are 4.7 k/ohm. The resistance of the third resistor R 3  is 3.9 k/ohm. 
         [0012]    The second comparison circuit  200  includes a second comparator U 2 , a fifth resistor R 5 , a sixth resistor R 6 , a seventh resistor R 7  and an eighth resistor R 8 . An inverting input terminal of the second comparator U 2  is grounded via the fifth resistor R 5 . The inverting input terminal of the second comparator U 2  is adapted to receive the third DC voltage via the sixth resistor R 6 . A non-inverting input terminal of the second comparator U 2  is grounded via the seventh resistor R 7 . The non-inverting input terminal of the second comparator U 2  is adapted to receive the third DC voltage via the eighth resistor R 8 . The second terminal of the thermocouple  500  is electrically connected to a connection point between the fifth resistor R 5  and the sixth resistor R 6 . An output terminal of the second comparator U 2  is adapted to output the second control signal. In one embodiment, a resistance of the fifth resistor R 5  is greater than a resistance of the seventh resistor R 7 . Resistances of the fifth resistor R 5 , the sixth resistor R 6  and the eighth resistor R 8  are 4.7 k/ohm. The resistance of the seventh resistor R 7  is 12 ohm. 
         [0013]    The switch circuit  300  includes a first MOSFET Q 1 , a second MOSFET Q 2  and a ninth resistor R 9 . Grids of the first MOSFET Q 1  and the second MOSFET Q 2  are electrically connected to the output terminal of the second comparator U 2 . A source of the first MOSFET Q 1  is grounded. A drain of the first MOSFET Q 1  is electrically connected to the output terminal of the first comparator U 1 . A grid of the second MOSFET Q 2  is grounded via the ninth resistor R 9 . A drain of the second MOSFET Q 2  is adapted to receive a fourth DC voltage. In one embodiment, the first MOSFET Q 1  and the second MOSFET Q 2  are N-channel MOSFETs. The fourth DC voltage is +6V. 
         [0014]    The indication circuit  400  includes a first LED D 1 , a second LED D 2  and a buzzer LS. An anode of the first LED D 1  is electrically connected to the output terminal of the first comparator U 1 . A cathode of the first LED D 1  is grounded. An anode of the second LED D 2  is electrically connected to the output terminal of the second comparator U 2 . A cathode of the second LED D 2  is grounded. An anode of the buzzer LS is electrically connected to the source of the second MOSFET Q 2 . A cathode of the buzzer LS is grounded. 
         [0015]    In a working state, when the thermocouple  500  is not connected to the test apparatus, a voltage level at the inverting input terminal of the first comparator U 1  is greater than a voltage level at the non-inverting input terminal of the first comparator U 1 . The output terminal of the first comparator U 1  is adapted to output a low voltage level first control signal. A voltage level at the inverting input terminal of the second comparator U 2  is greater than a voltage level at the non-inverting input terminal of the second comparator U 2 . The output terminal of the second comparator U 2  is adapted to output a low voltage level second control signal. The first LED D 1  and the second LED D 2  both do not emit light. 
         [0016]    A resistance of the thermocouple  500  is 30-100 ohm when a normally welded thermocouple  500  is connected to the test apparatus. A parallel resistance of the thermocouple  500  and the first resistor R 1  is less than 100 ohm. The voltage level at the inverting input terminal of the first comparator U 1  is less than the voltage level at the non-inverting input terminal of the first comparator U 1 . The output terminal of the first comparator U 1  is adapted to output a high voltage level first control signal. The first LED D 1  emits light. The voltage level at the inverting input terminal of the second comparator U 2  is greater than the voltage level at the non-inverting input terminal of the second comparator U 2 . The output terminal of the second comparator U 2  is adapted to output the low voltage level second control signal. The second LED D 2  does not emit light. 
         [0017]    When a short circuit welded thermocouple  500  is connected to the test apparatus, a resistance of the thermocouple  500  is less than 10 ohms. A parallel resistance of the thermocouple  500  and the fifth resistor R 5  is less than 10 ohms. The voltage level at the inverting input terminal of the second comparator U 2  is less than the voltage level at the non-inverting input terminal of the second comparator U 2 . The output terminal of the second comparator U 2  is adapted to output a high voltage level second control signal. The second LED D 2  emits light. The grid of the second MOSFET Q 2  is adapted to receive the high voltage level second control signal. The second MOSFET Q 2  turns on. The buzzer LS is adapted to receive the +6V fourth DC voltage to alarm. The grid of the first MOSFET Q 1  is adapted to receive the high voltage level second control signal. The first MOSFET Q 1  turns on. The voltage level of the first control signal at the output terminal of the first comparator U 1  is pulled down to the low voltage level. The first LED D 1  does not emit light. When an open circuit welded thermocouple  500  is connected to the test apparatus, a resistance of the thermocouple  500  is infinite. The working status of the first comparator U 1  and the second comparator U 2  is similar to when the thermocouple  500  is not connected to the test apparatus. The first LED D 1  and the second LED D 2  both do not emit light. 
         [0018]    Even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.