Hướng dẫn về cặp nhiệt điện (Thermocouple) đo nhiệt độ | Cung cấp thiết bị đo nhiệt độ

though this is Peter Weyland her I'dlike to welcome you to the new I hope will be the first to have numberI've tutorial videos that we're going to be producing herecontrol engineering I'd like to welcome you to the controlengineering test kitchens better known as my basement what are thethings that I've found in the work that I've done for control engineering is that it's hard to find something thatgets as much involvement for readers as temperature sensors every time I'vewritten something on the topic of thermocouples or RTD'sor whatever there's no shortage of customers andreaders that you're right back to me and say you know that tell me that have eithersaid something good or I said something bad arrive told something that's a simplificationand by Galia you know their product can do exactlywhat I said really care Peter so one of the first things I thought Iwould deal with is the topic thermocouples because that's one that I think early onI said you know that's one type of technologythat you could produce by yourself if you had to using thingsthat you can buy it your typical hardware store so what are the first things that I wantto do is demonstrate the concept a thermocouple using just literally some things that I found lyingaround here in the basement her for subject here is a thermocouplemade was just some wire that I had somenumber 12 steel wire with some number 12 solidcopper wire wrapped around it this is just your everyday Radio Shackadditional poom but one other things that it does haveits for useful for us is a range that greets from 0 to 300millivolts and given that thermocouples put up verylow voltage is we need something that magnitude to be able to read the signalssee can see that I've clicked to thermocouple wires there the blackone goes to the steel wire the red line goes to the copper wire I don't know if I've got the polarityright but will see that and just seige that's what we need now is a source ofheat turn on my and the propane torture laid on the table where the flame is hitting the to the wire so those twopieces of wire take the heat away now and see whathappens cools so simply by heeding those two pieces awire we created a voltage and now as thewires cooling considered going to wasn't much of avoltage was just over about one-and-a-half millivolts thus a voltagein on the lesson you'll see that the voltage changes goes down as the wire cools thermocoupletakes advantage of the fact that every kind of wire ever kinda metal does not have the same Seebeck effect sothat different materials will create adifferent voltage for the same temperature gradient let'stry slightly more sophisticated setup using some actual thermocouple wire thewires that are coming out of the crock pot and you can see coming around thetable attached to the alligator clips her actual typed T thermocouple wires they were given to us by the nice folksat more industries for this demonstration thereare two kinds of wire the red wire is actually a copper nickel Hellboy and the blue wire is just plain copper so what we've doneis we've put this now into the pot and you can see as the water warms up you have to take my word for that wateris warming up that the voltage is increasing on the readout its up to 1.

1 Bowl millivolt now it's up to 1.

2 mil ableshas the water gets harder the voltage you see from a thermocoupleis the voltage difference between the two different wires with theircorresponding Seebeck coefficients in other words the two different hellowires produce different voltages for the same temperature gradient thelarger the difference the easier it is to measure we call thepoint where the wires join a junction and that is the point where themeasurement is taken even though the voltage is generated anywhere on thewire where there is a gradient well thissetup produces a voltage all I can do is tell you the temperaturedifferential between the hot and cold and so the wires not an actual temperature reading to geta meaningful temperature measurement you have to know the reading at one endor the other we have to make one at the junctions a reference junction at unknowntemperature so in order to get the thermocouple to be able to give you an absolute temperature reading you haveto be able to introduce unknown temperature into the circuitsomewhere now if you look at our little crock potover here you'll notice that there is in fact steam coming out of it because the wateris getting very close to boiling fact it's kind of his boiling now then you'llnotice next to that there's a glass of ice water now notice that the red wire you can seehere coming around there goes from part tothe ice water that's our that's our copper nickel wire the blue wire is the this blue wire here is the copper wire whichgoes to the alligator clip and this white wire here is also copperwire which goes to the other alligator clipthen we're showing the reading on the voom we areup to formidable its with the water and the crockpot had a fullboil and the other end of the wire in the ice water now according to a typed T thermocoupletable with the reference junction in the icewater and the boiling water at 212 degreesFahrenheit we should be getting here eating exactly 4.

25 3 millivolts given that we are at theabsolute lowest and %uh this rather unsophisticated meter the factthat we're at 4.

0 I think we're doing really well now if we were to turn off the cooker slit sleeve this for a few minutes andcome back and see what the voltage reading as you can seeis already beginning to drop the case the water and a littleCrockwell has been calling now for a little bit so let's take a look and see what thevoltage reading is now the water is beginning to cool off you can see it still steaming a bit it's harder than i'd wanna stick myfinger and but it has cooled off somewhat the voltagereading will continue to fall along with the temperature according tothe chart now a 2.

4 million volts are temperature should be somewhere in the vicinity of about or 130 to 140degrees so that feels about right I don't reallywanna plunge my hand in there but it's not going to scold me eitherthis works but obviously wouldn't be practical andan actual field installation to have a cup of ice water is yourreference junction so in a typical Ohio situation or a I N A thermocouple transmitter you could use some other temperaturedevice to provide the reference temperature typically thermistor in most applications so let'sput this to a little more practical use given author slightly rainy Memorial Day3.

2 million volts it's like we're almost done here thecontrol engineering this is Peter Weyland her process industries editor thanks for watching.