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The way the potentiometer measures

  1. May 11, 2013 #1
    I may have a misconception about the way the potentiometer measures thermal emf... (Seebeck effect... Fe,Cu...the two points where these two wire are connected are at different Temperature... So there is a voltage difference between the two points...)

    When we are to measure the E,we need to know the current that goes through the resistance of the potentiometer wire while the galvanometer has to show that there is no current going through the thermocouple... Now the I that is flowing through the circuit of the potentiometer is divided into two parts for say Ip and Ic when it comes to the point where the thermocouple is connected... And we connected the jockey in such a way with the circuit that the thermal current equals Ic... So in the other part of the circuit does only Ip flow? So to get this reading should I connect the ammitter in this part of the circuit(The part where current enters the battery)? Will I get a different reading if I put the ammitter in the first part of the circuit(part where current is coming out of the battery)...
     
  2. jcsd
  3. May 11, 2013 #2
    I read the opening paragraph and had to stop. You lost me right from the start. A pot doesn't measure anything. A pot is a variable resistor that changes the current into a quantitive amount that is interpreted by whatever
     
  4. May 11, 2013 #3
    Moving to the second paragraph. Typically a pot used in the manner you are describing the voltage is given and well known and almost always 10 VDC. We know E and R so we can then calculate I. Most RTDs (the thermocouple) are exactly that an RTD a resistive thermal device. It requires no E or I and simply the information it relates back to the instrument calculates the value you call heat. As heat increases or decreases the reistance of the RTD changes.
     
  5. May 12, 2013 #4
    A potentiometer is a measuring instrument making use ( usually) of a wire 1m long.
    A pd exists across the wire and a "balance" can be found with the unknown voltage by means of a galvanometer.
    I think this is what the OP is referring to.....not potentiometers in the sense of "volume controls"
     
  6. May 12, 2013 #5
    Yeah, I seen your reply you must have edited it? I think there is a more plausible explination that you have questions about a pot.

    Allow me to offer a couple of caveats.

    Since I don't know the type of RTD you are utilizing I will say that polarity is essential in many common types. If you reverse, your device will not function properly. Types J and R will 100% not function in reverse polarity.

    Second, there also seems to be a great deal misconceptions concering the use of a DMMs (digital multimeters). Many toss around words like "series" but are actually in parallel. If you attemp to measure mAs in parallel I assure you something is going to be damaged. Since the fuse embedded in DMMs is typically 10 A it most likely wont be the DMM. Generally, people parallel amps on larger circuits (unwittingly) and for several reasons (which I wont bore you with) nothing gets damaged. mAs circuits are more sensitive so I promise something will get damaged.

    Anyway, I suggest you consult a glossary, dictionary, encyclopedia and get some definitions about several of the terms you mention.

    Somebody at this forum will be delighted to help you, so just post a reply when you are ready.
     
  7. May 12, 2013 #6
    Let us consider a circuit... There's a 10 V battery... A Rh(resistor with changeable resistance) and another battery is connected in parallel in the circuit... Now current I from the 10 V battery divides into two parts when it goes through the parallel connection... Let's note them by Ir and Ib... Now I change the Rh to some degree that the current from the other battery equals Ib...

    Clearly if we connect the ammeter to the front of the 10V battery it will read I... If we connect it to any of the two(Rh or battery) which are in parallel it will read either Ir or Ib... My ques is if I connect the ammeter to the back of the 10 V battery what reading will we get? Ir or I?

    And I knew that potentiometer is not itself a circuit(hence not a measuring device in this sense)... We have to connect it to a circuit... But as a circuit is not a measuring device,the pot allows us to measure V,so I wrote otherwise in that sense... Sorry for that...
     
  8. May 12, 2013 #7
    And I must confess that my use of 'terms' is really poor... I feel no discomfort reading physics in English but have trouble expressing as I don't use them much...
     
  9. May 14, 2013 #8
    Can someone please tell me what will be the reading? Ir or I?
     
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