RTD in detail tutorial explaining 2 Wire RTD , 3 Wire RTD and 4 Wire RTD
Summary
TLDR本期视频由calibration Academy频道带来,主题是电阻温度探测器(RTD)。视频将讲解RTD中的引线电阻是什么,为何三线RTD比二线RTD更准确,以及四线RTD如何更胜一筹。最后,将展示如何将RTD连接到温度变送器。通过Wheatstone桥式电路分析引线电阻对测量误差的影响,并解释三线和四线RTD如何减少这种误差。四线RTD通过电压信号而非电阻来测量温度,提供更高精度。视频还介绍了四线RTD的优点和缺点,并指导如何将不同线型的RTD连接到温度变送器。
Takeaways
- 🔍 视频介绍了电阻温度探测器(RTD)的相关知识。
- 🔌 讲解了二线RTD中的引线电阻及其对测量误差的影响。
- 📉 引线电阻会随着RTD和温度变送器之间距离的增加而增加测量误差。
- 🌡️ 通过惠斯通电桥原理解释了二线RTD的工作原理和误差产生。
- 📈 通过实例演示了正确测量和引线电阻导致的测量误差。
- 🔌 三线RTD通过额外的引线消除了电路中的有效引线电阻,比二线RTD更常用于工业中。
- 🔄 三线RTD通过惠斯通电桥方程,使得引线电阻在电路中相互抵消,提高了准确性。
- 🔌 四线RTD基于电压信号而非电阻测量温度,因此比二线和三线RTD更准确。
- 💡 四线RTD的优点包括更高的准确性和不受引线电阻影响,常用于需要精确温度读数的实验室。
- 🔋 四线RTD的缺点包括成本较高和长时间使用可能因自热产生小量测量误差。
- 🔧 视频还展示了如何将二线、三线和四线RTD连接到温度变送器。
Q & A
什么是RTD的引线电阻?
-引线电阻是指在实际应用中,连接RTD和温度变送器的电缆本身所具有的电阻,这部分电阻会加到RTD的电阻上,从而引入测量误差。
为什么三线RTD比二线RTD更准确?
-三线RTD通过使用额外的引线来消除电路中的有效引线电阻,这样可以避免二线RTD中因引线电阻而产生的测量误差。
四线RTD为什么比二线和三线RTD更准确?
-四线RTD基于电压信号而非电阻来测量温度,通过测量通过RTD的恒定电流和电压降来确定温度,因此不受引线电阻的影响。
如何将RTD连接到温度变送器?
-根据RTD的线数,将相应的电缆连接到温度变送器的指定端子上,二线RTD连接到端子4和5,三线RTD连接到端子4、5和6,四线RTD连接到端子3、4、5和6。
为什么测量误差会随着RTD和温度变送器之间距离的增加而增加?
-因为引线电阻会随着电缆长度的增加而增加,这会导致测量误差的增加。
在惠斯通电桥中,RTD的电阻是如何影响测量的?
-在惠斯通电桥中,RTD的电阻与引线电阻一起被测量,如果电桥不平衡,就需要考虑引线电阻对测量结果的影响。
为什么在三线RTD中需要使用等长的引线?
-使用等长的引线可以确保两边的引线电阻相互抵消,避免因引线电阻不同而引入额外的测量误差。
四线RTD的优点是什么?
-四线RTD的优点包括更高的测量精度,不受引线电阻影响,适用于需要精确温度读数的实验室环境。
四线RTD的缺点有哪些?
-四线RTD的缺点包括成本较高,长期使用可能会因为自热效应而产生小量的测量误差。
如何避免在四线RTD中因自热效应而产生的测量误差?
-通过优化温度变送器的设计,减少电流通过时产生的热量,可以降低自热效应对测量结果的影响。
Outlines
🔍 两线RTD的引线电阻及其误差分析
本段介绍了两线RTD(热敏电阻)的引线电阻问题。在实际应用中,RTD和温度变送器通常安装在不同位置,使用两线或三线电缆连接。这些电缆的电阻会与RTD的电阻相加,导致测量误差。文中通过电路图和方程式解释了引线电阻如何影响测量结果,并举例说明了在不同情况下,引线电阻如何导致温度读数的错误。例如,使用TDPT100测量200摄氏度时,如果直接测量RTD端子的电阻,可以得到正确的175.85欧姆的读数。但如果使用1欧姆的引线电阻,测量结果将变为177.85欧姆,导致温度读数错误为205.4摄氏度,误差为5.4摄氏度。
🔧 三线RTD的工作原理及其优势
三线RTD通过使用第三个引线来消除电路中的引线电阻影响,从而提高测量的准确性。文中通过惠斯通电桥方程解释了三线RTD如何通过两个引线电阻相互抵消来减少误差。同时强调了选择等长引线的重要性,以避免因引线电阻不同而产生的测量误差。此外,还讨论了三线RTD在工业中的普遍应用,以及其相对于两线RTD的优势。
🌡 四线RTD的工作原理及优缺点
四线RTD基于电压信号而非电阻来测量温度,因此比两线和三线RTD更为准确。文中通过图解和欧姆定律解释了四线RTD的工作原理,即通过测量电阻两端的电压降来确定温度。四线RTD的优点包括更高的测量精度和不受引线电阻影响的能力,使其适用于需要精确温度读数的测试实验室。然而,四线RTD的缺点包括成本较高和长期使用可能因自热效应而产生小量测量误差。此外,还介绍了四线RTD与温度变送器的连接方法。
🔌 RTD与温度变送器的连接方法
本段提供了不同类型RTD(两线、三线和四线)与温度变送器的连接方法。详细说明了每种RTD应连接到变送器的哪些端子,以及如何进行连接。例如,两线RTD连接时使用红白两色电缆分别连接到变送器的4号和5号端子;三线RTD则使用两个红色电缆连接到5号和6号端子,白色电缆连接到4号端子;四线RTD则需要连接两个红色和两个白色电缆到相应的端子。连接完成后,打开回路电源并检查变送器的显示读数。
Mindmap
Keywords
💡电阻温度探测器
💡引线电阻
💡惠斯通电桥
💡三线RTD
💡四线RTD
💡欧姆定律
💡温度变送器
💡测量误差
💡自加热
💡恒定电流源
💡连接方式
Highlights
本视频介绍了电阻温度检测器(RTD)的相关知识,包括导线电阻对测量精度的影响以及不同类型RTD的准确性比较。
在实际应用中,RTD和温度变送器通常安装在不同位置,使用两线或三线电缆连接,这些电缆的电阻会影响RTD的测量结果。
两线RTD的导线电阻会与RTD的电阻相加,导致测量误差,这种误差随着RTD与温度变送器之间距离的增加而增大。
惠斯通电桥的平衡方程式显示了导线电阻如何引入测量误差。
通过实例演示了在没有导线电阻的情况下,RTD的测量结果如何准确反映温度。
工业应用中,导线电阻的存在会导致测量误差,例如,当使用1欧姆的导线连接RTD时,会导致5.4摄氏度的误差。
三线RTD通过额外的导线消除了电路中的有效导线电阻,这是两线RTD无法做到的,因此三线RTD在工业中更常用。
三线RTD的惠斯通电桥方程式显示了导线电阻如何相互抵消,从而提高了测量的准确性。
四线RTD基于电压信号而非电阻测量温度,因此比两线和三线RTD更准确。
四线RTD通过恒定电流源和测量电压降来测量温度,电流值保持恒定,因此不会影响电压降。
四线RTD的优点包括更高的测量精度和不受导线电阻影响,常用于需要精确温度读数的实验室。
四线RTD的缺点是成本较高,长期使用可能因自热效应产生小幅度的测量误差。
介绍了两线RTD变送器的连接方法,包括电源和传感器输入的接线方式。
展示了三线RTD与温度变送器的连接过程,包括如何连接红白三根电缆。
解释了四线RTD与温度变送器的连接方式,包括四根电缆的连接方法。
视频最后感谢观众观看,并鼓励观众如果有疑问在评论区提问。
Transcripts
Hello friends welcome back to my channel
calibration Academy
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my today's video is on resistor
temperature detector
in this video you will learn
what is lead wire resistance in RTD
secondly you will learn why three wire
RTD is more accurate than two-wire RTD
in addition to this you will also learn
why four wire RTD is more accurate than
the two wire and three-wire RTD
and in last part of video I'm going to
explain how to connect RTD to
temperature transmitter
so please watch this video till the end
so let's learn what is lead wire
resistance in two-wire RTD
as we know that in practical application
RTD and temperature transmitter is
mounted at different locations
so we use two wire or three wire cables
to connect our TV and temperature
transmitter
these two wire or three wire cables has
also its own resistance which gets added
in the resistance of the RTD
these two wire or three wire cables
resistance is known as lead wire
resistance
these lead wires produce measurement
error and temperature reading which I'm
going to explain in next slide
as you can see from circuit diagram of
two wire RTD lead wire resistance gets
added in the resistance of the RTD and
because of lead wire the measurement
error also increases
the measurement error increases with
increase of distance between the
temperature transmitter in the RTD
position
in this circuit diagram R1 R2 and R3 are
wheatstone bridge resistors
and our lead is the resistance of that
particular lead wires
and RT is the resistance of RTD
as you can see this is an equation of
wheatstone bridge when it is in Balance
condition
in this equation RX is the sum of RT and
two lead wire resistance
so it can be clearly seen from above
equation that the lead resistance
introduce error in measurement
let's understand this thing by taking
two examples
as you can see in this example we have
taken our tdpt100 and the temperature
coefficient of this RTD is 0.00385
now let's assume that we are measuring
the resistance directly at the terminals
of two wire RTD
in other words we are measuring the
resistance without any lead wires
after this put the RTD in temperature
bath and set temperature of temperature
bath to 200 degrees Celsius
and measure the resistance of RTD at its
terminals you should get
175.85 ohm resistance which is correct
measurement
in other words the measured resistance
of RTD shows the correct temperature
readings
let's take one more example to
understand lead wire resistance in
detail
and Industry applications we use a cable
to connect the RTD to the temperature
transmitter
this cable resistance is known as lead
wire resistance and it will add to the
total resistance
for example if we use two lead wires to
connect our TD to temperature
transmitter and if each lead wire
resistance is 1 ohm
and if we put all these values in this
equation then we will get
177.85 ohm resistance value
in this example the temperature
according to the total resistance value
is 205.4 degrees Centigrade which is in
correct temperature
and if we calculate error we will get
5.4 degrees Celsius error
in other words the lead resistance
introduced measurement error of 5.4
degrees Centigrade
done
RTD is that freewire RTD has extra lead
wire
and this extra lead wire eliminates the
effective lead resistance in circuit
which is not possible in two-wire RTD
hence this is a reason that three-wire
RTD is most commonly used RTD in the
industries
now let's understand in detail that Y3
wire RTD is more accurate than two wire
RTD
as you can see this is wheatstone Bridge
equation for three-wire RTD
in this equation numerator and
denominator both have our lead and
because of this right hand side ratio
does not get affected due to lead
resistance
in other words both lead resistors
eliminates each other effects in circuit
however both lead wires should have
equal lengths to avoid lead resistance
effect in the circuit
as you can see this is an equation when
wheatstone Bridge Is In Balance
condition
in this equation lead resistance will be
canceled each other with help of a third
lead wire
and this is a reason that the
temperature measurement does not get
affected due to lead resistance
however as I said earlier great care
need to be taken to choose equal lengths
of lead wires
in other words if you do not choose
equal length lead wires temperature
measurement error will occur
done
let's understand the operating principle
of four wire RTD
four wire RTD measures the temperature
based on the voltage signal instead of
resistance and this is reason that four
wire RTD is more accurate than two wire
and three-wire RTD
let's understand this thing with the
help of this diagram
as you can see from the picture that
four wire RTD is constant current Source
in series with the two lead wires
and the voltage drop is measured across
the another two lead wires
Ohm's law states that voltage drop
across resistor is directly proportional
to current and resistance value of that
resistor
so in this equation current value will
remain constant or very minimum because
of constant current source
in other words current value does not
affect voltage drop across resistor
and the voltage will be generated based
on the change in resistance which
depends on the measured temperature
in other words RTD resistance will
change with temperature change and it
will change voltage drop across two lead
resistors
hence temperature is measured based on
voltage drop across two lead resistors
now let's learn what are the pros and
cons of four wire RTD
first of all let's understand what are
the advantages of having four wire RTD
firstly four wire RTD reads more
accurate than the two wire and
three-wire RTD
and it is commonly used in test
Laboratories where exact temperature
readings are required
secondly four-wire RTD does not get
affected by lead wire resistance
and this is a reason that it gives High
degree of accurate temperature
measurement
there are a few drawbacks of having four
wire RTD
first drawback is that four wire RTD is
more expensive than the two wire and
three-wire RTD
in addition to this if you use four wire
RTD for long period of time it will
produce small amount of measurement
error because of self-heating
structure of temperature transmitter
terminal number one and terminal number
two are for power supply
in other words Loop power supply will be
connected to terminal number 1 and
terminal number two
and terminal number three four five and
six are used for RTD sensor input
as name suggests two-wire transmitter
has two cables one cable is red and
other cable is white
to connect two wire RTD to temperature
transmitter connect red cable to
terminal number five
and connect white cable to terminal
number four of temperature transmitter
in this section I am going to show how
to connect three wire RTD to temperature
transmitter
as name suggests three wire RTD has
three cables
two red cables and one white cable
to connect three wire RTD to temperature
transmitter connect one of the red cable
to terminal number five
and another red cable to terminal number
six
after this connect white cable to
terminal number four of temperature
transmitter
once you are done with RTD connection
turn on Loop power supply and check the
reading on display
in this section I am going to show four
wire RTD connection with temperature
transmitter
as name suggests four wire RTD has four
cables
two red cables
and two white cables
to connect four wire RTD with
temperature transmitter connect one of
the red cable to terminal number five
and another red cable to terminal number
six
after this connect one of the white
cable to terminal number three and
another white cable to terminal number
four of temperature transmitter
once you are done with connection turn
on Loop power supply and check the
reading on display of transmitter
thank you friends for watching this
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