Component - Thermocouple V1.10

PSoC® Creator™ Component Datasheet
Thermocouple Calculator
1.10
Features
 Supports B, E, J, K, N, R, S, and T Type Thermocouples
 Provides functions for thermo-emf to temperature and temperature to
voltage conversions

Displays Calculation Error Vs. Temperature graph
General Description
In thermocouple temperature measurement, the thermocouple temperature is calculated based
on the measured thermo-emf voltage. The voltage to temperature conversion is characterized by
the National Institute of Standards and Technology (NIST), and NIST provides tables and
polynomial coefficients for thermo-emf to temperature conversion. The NIST tables and
polynomial coefficients can be found in the following link:
http://srdata.nist.gov/its90/download/download.html
Thermocouple temperature measurement also involves measuring the thermocouple reference
junction temperature and converting it into a voltage. The Thermocouple Calculator component
simplifies the thermocouple temperature measurement process by providing APIs for thermo-emf
to temperature conversion and vice versa for all thermocouple types mentioned above, using
polynomials generated at compile time. The thermocouple component evaluates the polynomial
in an efficient way to reduce computation time.
When to Use a Thermocouple Calculator
The component has only one use case. The component provided API is used to convert thermoemf to temperature and vice versa.
Input/Output Connections
This component is a software component and doesn’t have any input/output connections.
Cypress Semiconductor Corporation • 198 Champion Court • San Jose, CA 95134-1709 • 408-943-2600
Document Number: 001-84997 Rev. **
Revised December 3, 2012
Thermocouple Calculator
PSoC® Creator™ Component Datasheet
Parameters and Settings
Drag a Thermocouple Calculator component onto your design and double-click it to open the
Configure dialog. This dialog has one tab to guide you through the process of setting up the
Thermocouple Calculator component.
General Tab
The General tab provides the following parameters.
Thermocouple Type
This field allows user selection of the thermocouple type.
Calculation error budget
The user selects the maximum error allowed due to polynomial computation. This is the error
only for temperature greater than -200 °C.
Temperature Error Vs Temperature graph
This graph shows the temperature error vs. temperature for the thermocouple type and
polynomial.
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Document Number: 001-84997 Rev. **
PSoC® Creator™ Component Datasheet
Thermocouple Calculator
Polynomial
Displays the order of polynomial that is used for calculations in GetTemperature() API.
Three types of polynomials are used:



NIST (provided by the National Institute of Standards and Technology)
7th order (approximation of NIST polynomial)
5th order (approximation of NIST polynomial)
The polynomial is chosen based on the selected error budget. The polynomial with the lowest
order which does not exceed the error budget is selected.
CPU cycles
An estimate of the total number of CPU cycles taken for computing the selected polynomial is
displayed.
Max error table
The table contains the maximum temperature error for given temperature range for the selected
thermocouple type and polynomial.
Application Programming Interface
Application Programming Interface (API) routines allow you to configure the component using
software. The following table lists and describes the interface to each function. The subsequent
sections cover each function in more detail.
By default, PSoC Creator assigns the instance name "Thermocouple_1" to the first instance of a
component in a given design. You can rename it to any unique value that follows the syntactic
rules for identifiers. The instance name becomes the prefix of every global function name,
variable, and constant symbol. For readability, the instance name used in the following table is
"Thermocouple".
Function
Description
int32 Thermocouple_GetTemperature(int32 voltage)
Calculates the temperature from thermo-emf in V
int32 Thermocouple_GetVoltage(int32 temperature)
Calculates the voltage given the temperature in
1/100ths degrees C. Used for calculating the cold
junction compensation voltage based on the
temperature at the cold junction.
Document Number: 001-84997 Rev. **
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Thermocouple Calculator
PSoC® Creator™ Component Datasheet
int32 Thermocouple_GetTemperature(int32 voltage)
Description:
Calculates the temperature from thermo-emf in V.
Parameters:
Voltage, in V.
Return Value:
Temperature in 1/100ths degrees C
Side Effects:
None
int32 Thermocouple_GetVoltage(int32 temperature)
Description:
Calculates the voltage given the temperature in 1/100ths degrees C. Used for
calculating the cold junction compensation voltage based on the temperature at the cold
junction.
Parameters:
Temperature in 1/100ths degrees C
Return Value:
Thermo-emf voltage in V.
Side Effects:
None
MISRA Compliance
This section describes the MISRA-C:2004 compliance and deviations for the component. There
are two types of deviations defined:


project deviations – deviations that are applicable for all PSoC Creator components
specific deviations – deviations that are applicable only for this component
This section provides information on component-specific deviations. Project deviations are
described in the MISRA Compliance section of the System Reference Guide along with
information on the MISRA compliance verification environment.
The Thermocouple Calculator component has not been verified for MISRA-C:2004 coding
guidelines compliance.
Sample Firmware Source Code
PSoC Creator provides many example projects that include schematics and example code in the
Find Example Project dialog. For component-specific examples, open the dialog from the
Component Catalog or an instance of the component in a schematic. For general examples,
open the dialog from the Start Page or File menu. As needed, use the Filter Options in the
dialog to narrow the list of projects available to select.
Refer to the “Find Example Project” topic in the PSoC Creator Help for more information.
Page 4 of 11
Document Number: 001-84997 Rev. **
PSoC® Creator™ Component Datasheet
Thermocouple Calculator
Functional Description
In 1821, Thomas Seebeck, an Estonian-German physicist discovered that when two dissimilar
metals are connected, as shown in Figure 1(a), and one of the junctions is heated, there is a
continuous flow of current through the loop. When the loop is broken and the voltage is
measured (see Figure 1(b)), the measured voltage is directly related to the temperature
difference between the two junctions. This phenomenon where a voltage is produced because of
the heating of the junction of two metallic conductors is called thermoelectric effect or Seebeck
effect. The junction where heat is applied is called the hot or measurement junction. The other
junction is called the cold junction or reference junction, and the voltage developed is called
thermo-emf.
Figure 1(a). Thermocouple – Seebeck Effect
Figure 1(b). Thermocouple –Seebeck Effect
The thermo-emf depends on the following:



Metals used at the junction
The temperature difference between the hot and cold junctions
The absolute value of the cold junction temperature. That is, the thermo-emf produced for hot
junction temperature of 100 °C and cold junction temperature of 0 °C will be different from the
thermo-emf produced for hot junction temperature of 800 °C and cold junction temperature of
700 °C even though the temperature difference in both cases is 100 °C.
Depending on the types of metals used, thermocouples can be classified into multiple types. The
types of thermocouples differ in their temperature range of operation and sensitivities (voltage
change per unit change in temperature, V/°C). Two major standards, IEC EN 60584-2 and ASTM
E230, govern the thermocouple tolerance. The tolerance specifies the maximum error due to
replacing one thermocouple with another of the same type.
Table 1 lists some of the popular thermocouple types, their metal combination, temperature
ranges, sensitivities, and their tolerances according to ASTM standard. As shown in Table 1,
Document Number: 001-84997 Rev. **
Page 5 of 11
Thermocouple Calculator
PSoC® Creator™ Component Datasheet
ASTM establishes two thermocouple tolerance standards, standard and special. Tolerance
standards are not defined in the whole temperature range.
The National Institute of Standards and Technology (NIST) provides the thermo-emf versus hot
junction temperature data for all thermocouple types for cold junction at 0 °C. Cold junction
temperature of 0 °C is chosen as reference because the thermo-emf is 0 V at 0 °C. An ice bath
usually provides the 0 °C reference temperature. NIST provides a table as well as polynomial
coefficients to convert thermo-emf to temperature and vice versa. Figure 2 shows a K-type
thermocouple heated at one junction and maintained at 0 °C in the other junction;
Figure 3 (on the next page) shows the thermo-emf versus hot junction temperature graph for a Ktype thermocouple for cold junction at 0 °C. The sensitivity of a K-type thermocouple can be
found from the NIST table and is approximately 40 V/°C for temperatures > -100 °C.
Figure 2. K-type Thermocouple with Cold Junction at 0 °C
+
Figure 3. Thermo-emf versus Temperature for K-type Thermocouple (Cold Junction at 0 °C)
Cold Junction Compensation
By measuring the thermo-emf using an ADC, we can easily determine the temperature. But there
is one catch; the cold junction has to be maintained at 0 °C to use the NIST tables. It is
impractical to provide an ice bath and in most cases the cold junction will be at ambient
temperature. If the cold junction temperature is not equal to 0 °C, the cold junction would also
develop a thermo-emf, V2, as shown in Figure 4, reducing the measured voltage, V. To properly
measure the hot junction temperature, the cold junction voltage, V 2, has to be added to the final
voltage, V.
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Document Number: 001-84997 Rev. **
PSoC® Creator™ Component Datasheet
Thermocouple Calculator
Figure 4. Cold Junction not at 0 °C
+
If we find the cold junction temperature, the voltage V 2 can be calculated from the NIST table.
Hence in cases where the cold junction is not at 0 °C, the cold junction temperature has to be
measured and the thermo-emf corresponding to that temperature has to be added to the
thermocouple voltage. This procedure is called cold junction compensation.
A thermistor, RTD, diode, or IC based sensor can be used for cold junction temperature
measurement. (Remember that one of these cold junction temperature measurement sensors
cannot substitute a thermocouple as they cannot be used for measuring very high temperatures
or used in corrosive or rugged environment).
Measuring Thermo-emf
Thermo-emf has to be measured with an ADC by connecting the input leads of the ADC to the
thermocouple as shown in Figure 5.
Figure 5. Measuring Thermo-emf
The input (copper) leads of the ADC form two more thermocouples (copper-alumel) adding two
more voltages, V3 and V4 to the equation. V3 and V4 are in opposite directions; they will have the
same magnitude as long as both the thermocouples are at the same temperature. Hence, we
need to ensure that both the copper-alumel thermocouples are at the same temperature so that
the thermo-emf remains unchanged.
Document Number: 001-84997 Rev. **
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Thermocouple Calculator
PSoC® Creator™ Component Datasheet
Table 1. Thermocouple Types
Thermocouple
Type
Metal Content in
Positive Leg
B
70.4% Platinum (Pt)
29.6% Rhodium (Rh)
E
90% Nickel (Ni)
10% Chromium (Cr)
Metal Content
in Negative Leg
Temp
Range (°C)
Sensitivity
at 25 °C
(µV/°C)
93.9% Pt, 6.1%
Rh
0 – 1820
0
800 – 1700
0.5%
55% Copper
(Cu)
-270 – 1000
61
-200 – 0
1.7 °C or 1%
0 - 900
1.7 °C or 0.5%
1°C or 0.4%
1.1 °C or 0.4%
45% Ni
Tolerance (ASTM)
Temp
Range (°C)
Standard
Special
J
99.5% Iron (Fe)
55% Cu, 45% Ni
-210 – 1200
52
0 – 750
2.2 °C or 0.75%
K
90% Ni
95% Ni
-270 – 1372
41
-200 – 0
2.2 °C or 2%
10% Cr
5% Various
elements
0 – 1250
2.2 °C or 0.75%
84.4% Ni, 14.2% Cr
95.5% Ni,
4.4% Si
-270 – 1300
-270 – 0
2.2 °C or 2%
1.4% Silicon
0 – 1300
2.2 °C or 0.75%
1.1 °C or 0.4%
R
87% Pt, 13% Rh
100% Pt
-50 – 1768
6
0 - 1450
1.5 °C or 0.25%
0.6 °C or 0.1%
S
90% Pt, 10% Rh
100% Pt
-50 – 1768
6
0 – 1450
1.5 °C or 0.25%
0.6 °C or 0.1%
T
100% Cu
55% Cu, 45% Ni
-270 – 400
41
-200 – 0
1 °C or 1.5%
0 – 350
1 °C or 0.75%
N
26
1.1 °C or 0.4%
0.5 °C or 0.4%
Resources
Component is implemented entirely in firmware. It does not consume any other PSoC resources.
API Memory Usage
The component memory usage varies significantly, depending on the compiler, device, number
of APIs used and component configuration. The following table provides the memory usage for
all APIs available in the given component configuration.
The measurements have been done with the associated compiler configured in Release mode
with optimization set for Size. For a specific design, the map file generated by the compiler can
be analyzed to determine the memory usage.
PSoC 3 (Keil_PK51)
Configuration
PSoC 5 (GCC)
Flash
SRAM
Flash
SRAM
Bytes
Bytes
Bytes
Bytes
Thermocouple B-type
710
0
336
0
Thermocouple E-type
730
0
344
0
Thermocouple J-type
702
0
324
0
Thermocouple K-type
730
0
340
0
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Document Number: 001-84997 Rev. **
PSoC® Creator™ Component Datasheet
Thermocouple Calculator
PSoC 3 (Keil_PK51)
Configuration
PSoC 5 (GCC)
Flash
SRAM
Flash
SRAM
Bytes
Bytes
Bytes
Bytes
Thermocouple N-type
899
0
436
0
Thermocouple R-type
911
0
464
0
Thermocouple S-type
895
0
444
0
Thermocouple T-type
706
0
324
0
Performance
The performance of the component depends on the implementation method chosen in the
customizer. The measurements below have been gathered using a CPU speed of 24 MHz, with
the associated compiler configured in Release mode. These numbers should be treated as
approximations and used to determine necessary trade-offs.
GetTemperature API
NIST polynomials
Thermocouple
Type
Voltage Range (mV)
Temperature
Range (°C)
B
0.033 to 0.291
100 to 250
7
7900
270
0.291 to 2.431
250 to 700
8
8500
270
2.431 to 13.820
700 to 1820
8
8500
270
-9.718 to -8.825
-250 to -200
9
9100
310
-8.825 to 0
-200 to 0
8
8500
310
0 to 76.373
0 to 1000
8
8500
310
-8.095 to 0
-210 to 0
8
8500
270
0 to 42.919
0 to 760
7
7900
270
42.919 to 69.553
760 to 1200
5
6700
270
-5.891 to 0
-200 to 0
8
8500
310
0 to 20.644
0 to 500
9
9100
310
20.644 to 54.886
500 to 1372
6
7300
310
-4.313 to -3.990
-250 to -200
9
9100
310
-3.990 to 0
-200 to 0
9
9100
310
E
J
K
N
Document Number: 001-84997 Rev. **
Polynomial
No. of CPU
No. of CPU
Order
Cycles (PSoC 3) Cycles (PSoC 5)
Page 9 of 11
Thermocouple Calculator
Thermocouple
Type
PSoC® Creator™ Component Datasheet
Voltage Range (mV)
Temperature
Range (°C)
0 to 20.613
0 to 600
7
7900
310
20.613 to 47.513
600 to 1300
5
6700
310
-0.226 to 1.923
-50 to 250
10
9700
340
1.923 to 13.228
250 to 1200
9
9100
340
13.228 to 19.739
1200 to 1664.5
5
6700
340
19.739 to 21.103
1664.5 to 1768.1
4
6100
340
-0.235 to 1.874
-50 to 250
9
9100
310
1.874 to 11.950
250 to 1200
9
9100
310
11.950 to 17.536
1200 to 1664.5
5
6700
310
17.536 to 18.693
1664.5 to 1768.1
5
6700
310
-6.180 to -5.603
-250 to -200
7
7900
240
-5.603 to 0
-200 to 0
7
7900
240
0 to 20.872
0 to 400
6
7300
240
R
S
T
Polynomial
No. of CPU
No. of CPU
Order
Cycles (PSoC 3) Cycles (PSoC 5)
Polynomials of 7th and 5th order
Polynomial
Order
No. of CPU
No. of CPU
Cycles (PSoC 3) cycles (PSoC 5)
7
7900
240
5
6700
170
GetVoltage API
Thermocouple type
Temperature range
(°C)
Polynomial order
No. of CPU
cycles (PSoC 3)
No. of CPU
cycles (PSoC 5)
B
0 to 100
6
7300
200
E
-20 to 100
8
8500
270
J
-20 to 100
7
7900
240
K
-20 to 100
8
8500
270
N
-20 to 100
8
8500
270
R
-20 to 100
7
7900
240
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Document Number: 001-84997 Rev. **
PSoC® Creator™ Component Datasheet
Thermocouple Calculator
S
-20 to 100
7
7900
240
T
-20 to 100
8
8500
270
Component Changes
This section lists the major changes in the component from the previous version.
Version
1.10
Description of Changes
Added MISRA Compliance section
Reason for Changes / Impact
The component was not verified for MISRA
compliance.
Added Sample Firmware Source Code section
1.0
Version 1.0 is the first release of the Thermocouple
Calculator component
© Cypress Semiconductor Corporation, 2012. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of
any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be used
for medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for
use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress products in lifesupport systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.
PSoC® is a registered trademark, and PSoC® Creator™ and Programmable System-on-Chip™ are trademarks of Cypress Semiconductor Corp. All other trademarks or registered trademarks
referenced herein are property of the respective corporations.
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foreign), United States copyright laws and international treaty provisions. Cypress hereby grants to licensee a personal, non-exclusive, non-transferable license to copy, use, modify, create
derivative works of, and compile the Cypress Source Code and derivative works for the sole purpose of creating custom software and or firmware in support of licensee product to be used only in
conjunction with a Cypress integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or representation of this Source Code except as
specified above is prohibited without the express written permission of Cypress.
Disclaimer: CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A HALFICULAR PURPOSE. Cypress reserves the right to make changes without further notice to the materials described herein.
Cypress does not assume any liability arising out of the application or use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in lifesupport systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress’ product in a life-support systems application
implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.
Use may be limited by and subject to the applicable Cypress software license agreement.
Document Number: 001-84997 Rev. **
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