Temperature
Used: It
is to be measure hotness and coldness of the body.
Units:
1.
Degree centigrade (0C)
2.
Degree Fahrenheit (0F)
3.
Degree kelvin (0K)
4.
Degree Rankin (0R)
Conversion for (0C) to (0F)
and (0F) to (0C)
Formula
0C = 0F-32/1.8
0F = (0C*1.8)
+32
E.g.
1000F =? 0C
0C = 0F-32/1.8
0C = 100-32/1.8
0C = 37.770C
|
1000C =? 0F
0F = (0C*1.8)
+32
0F = (100*1.8)
+32
0F = 2120F
|
100F =? 0C
0C = 0F-32/1.8
0C = 10-32/1.8
0C = -12.220C
|
-400C =? 0F
0F = (0C*1.8)
+32
0F = (-40*1.8)
+32
0F = -400F
|
What are the temp sensing elements?
1.
RTD (Resistance Temp Detector)
2.
Thermocouple
3.
Thermistor
1.
RTD (Resistance Temp Detector)
a.
RTD is a temp sensing element
b.
RTD is used for (10000C)
temp measurement
c.
Output of RTD is resistance
d.
RTD works on the principle of
“change in Resistance”.
e.
When temp changes, Resistance
also changes.
f.
When temp increases Resistance
also increases so that RTD is called positive temp co-efficient (PTC).
00C-----------------
------------------------- 100Ω
300C-----------------------------------------
111.6Ω
500C-----------------------------------------
119.4Ω
1000C-----------------
---------------------- 138.5Ω
1500C----------------------------------------
157.33Ω
2000C----------------------------------------
175.84Ω
3000C----------------------------------------
212.06Ω
Note:
-for accuracy used up to 3000C only.
Diagram of RTD
What is PT 100?
When temp is 00C then resistance
is 100Ω
Formula: - PT
100
RT = R0 x (1+αT)
Where
RT = Resistance
of temp to be measured.
R0 =
Resistance at 00C = 100Ω.
α = Temp
co-efficient = 0.00385
T = Temp
to be measured.
1000C =? Ω
RT = R0 x (1+αT)
RT = 100 x (1+0.00385 x 100)
RT = 100 x (1+0.385)
RT = 100 x 1.385
RT = 138.5 Ω
|
300C =? Ω
RT = R0 x (1+αT)
RT = 100 x (1+0.00385 x 30)
RT = 100 x (1+0.1155)
RT = 100 x 1.1155
RT = 111.55 Ω
|
1750C =? Ω
RT = R0 x (1+αT)
RT = 100 x (1+0.00385 x 175)
RT = 100 x (1+0.67375)
RT = 100 x 1.67375
RT = 167.375 Ω
|
Type of RTD:-
1.
Two wire RTD
2.
Three wire RTD
3.
Four wire RTD
1.
Two wire RTD
Diagram
Used for short distance
Distance up to 100 meter
Not accurate for long distance
2.
Three wire RTD
Diagram
Used for long distance
Distance up to 500 meter
Accurate for long distance
Note: - 3rd wire is used for “compensation”
of “resistance” (To cancel the resistance of cable or lead wire)
3.
Four wire RTD
Diagram
Used for very long distance.
Distance up to 1000 meter.
What is calibration?
Comparing measuring value with standard value
for its best accuracy.
Temperature
transmitter (TT)
TT is used for temperature measurement.
Calibration:-
Company
= Rosemount
Model
no = 244R
Range
= 0 to 2000C
Output
= 4 to 20 ma
Supply
= 24vdc
RTD
input PT 100 type.
Diagram
Calibration table:-
Ma output
|
Temp in 0C
|
Resistance in Ω
|
|
Zero (Z)
|
4
|
0
|
100Ω
|
8
|
50
|
119.4Ω
|
|
Linearity
|
12
|
100
|
138.5Ω
|
16
|
150
|
157.33Ω
|
|
Span (S)
|
20
|
200
|
175.84Ω
|
Calibration circuit: -
Diagram
How to calibrate temp transmitter (RTD input)
1.
Connect 24vdc to transmitter and connect
Multimeter in series with 24vdc supply.
2.
Connect resistance source at RTD input
terminal.
3.
Apply resistance from resistance source
according to range and check zero and span
4.
Check zero (4ma), if it is disturbed then
adjust it using zero pot or push button
5.
Checks span (20ma), if it is disturbed then
adjust it using span pot or push button.
6.
Check linearity by applying 50% input and
check transmitter output should be 12 ma
7.
Transmitter is calibrated ok
Temp transmitter (TT)
Calibration:-
Eample 2
Company
= Rosemount hart smart family.
Model
no = 644
Range
limit = -200 to 8500C
Input range = -50 to 1500C
Output = 4 to 20 ma
Supply voltage = 24vdc
RTD input PT 100 type
Diagram
Calibration table:-
Ma output
|
Temp in 0C
|
Resistance in Ω
|
|
Zero (Z)
|
4
|
-50
|
80.13Ω
|
8
|
0
|
100Ω
|
|
Linearity
|
12
|
50
|
119.4Ω
|
16
|
100
|
138.5Ω
|
|
Span (S)
|
20
|
150
|
157.33Ω
|
Formula:
NOTE: URV & LRV is given in input range i.e. -50 to 150
Therefore URV = upper range value i.e. 150
LRV = lower range value i.e. -50
1.
Connect 24vdc to transmitter and
connect Multimeter in series with 24vdc supply.
2.
Connect resistance source at RTD input
terminal.
3.
Apply resistance from resistance
source according to range and check zero and span
4.
Check zero (4ma), if it is disturbed
then adjust it using zero pot or push button
5.
Checks span (20ma), if it is
disturbed then adjust it using span pot or push button.
6.
Check linearity by applying 50%
input and check transmitter output should be 12 ma
7.
Transmitter is calibrated ok
