Formation the temperature rise in contactors. As per standards,

Formation of Synopsis

 

1. Objective of work

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The objective of
this project is to automate the temperature rise testing of contactors as per standards.

This is being
carried out in Salzer Electronics Ltd., Unit III (R&D sector).  

 

2. Motivation

Contactors are
electromechanical devices that are used to switch large amount of electrical
power through its contacts. 1
They are commonly used for controlling electric motors. Contactors heat up due
to resistive power dissipation through contacts. And this may cause the device
to burn. Thus, it becomes vital to test the temperature rise in contactors. As
per standards, this test has to be performed for 8 hours. And this laborious
and mundane task is being done manually in industries. Thus, with the help of
embedded systems, we can reduce the manual effort being put. By using a
microcontroller, we reduce a huge manual work load, and are creating an economic
and smart solution for this problem.

 

3. Target specifications if any

The
expected result of this project, is a system that will note the temperature
rise as per product testing norms, and give a beep if the temperature rise
crosses the threshold, and gives a different beep if the testing is successful.

 

4. Functional partitioning of project

Functionally, this project has been divided
into four sections.

Step
IThe first step, is to read the
ambient temperature and the temperature of a contactor pole using appropriate
sensors. Then, the temperature rise is to be calculated.4.2 Step IIThe next step is to compare this
rise to a threshold temperature, which is 48oC. If the temperature
rise crosses this within the 8 hour test period, give the “FAILURE” beep and
stop the test.4.3 Step IIIIf the temperature rise does not
cross the threshold temperature within the 8 hour test period, then give the
“SUCCESS” beep.4.4 Step IVIf the temperature rise is
constant for one hour, then we can give the “SUCCESS” beep and stop the test. 5. Methodology In this section, the bench set-up for manual
testing of temperature rise is sketched, the procedure adopted for the test is
discussed, and the initial steps towards automation, such as selection of
sensors, are elaborated.   5.1 Given
below is the circuit diagram of the bench set up of the manual testing of
temperature rise

Figure 1:
Bench Set-up of manual testing of temperature rise

 

5.2 Given below is the procedure adopted for the
temperature rise test:

   Note down the time. (tn)Note down the ambient temperature. (Ta)Note down the temperature of the contactor. (Tc)Take the difference. ( Tr = | Tc –
Ta | )If
this is less than the threshold tolerance temperature, i.e; 48oC, for 8 hours, or if it is  constant for at least one hour, the product is
said to be O.K. Else if it crosses the tolerance temperature within the test
period, the product is said to have failed this test. 5.3 Thermocouple and MAX31855 interface chip:While working
manually, the engineers in the testing sector made use of special bulky
instruments for precise measurement of temperature. For automating this test,
special sensors are required, which can take precise readings. A J-type
thermocouple 2 sensor has to
be used for this purpose. A thermocouple has no electronics inside of it.
Thermocouples are made by welding two metal wires. Because of a physical effect
of two joined metals, there is a slight but measurable voltage across them.
This voltage increases with temperature. This voltage is in the order of
microvolts. Thus a proper set of amplifiers, filters, ADCs, etc. are required
for a high resolution, low noise output. Hence, we can make use of a MAX31855
interface chip. This can be easily interfaced with various microcontrollers,
and are simple to use. 

Figure 2:
Pin Diagram of MAX31855 3

 

 

Tools requiredTemperature
rise test bench set-upThis set up includes:

Auto transformer (Input: 230V, 50Hz; Output:
0-300V; primary to secondary turn ratio= 1:2)Current transformer (100 to 5A current;
primary to secondary turn ratio = 1:20) ContactorsStandardized wires with respect to contactors

Thermocouple
Sensors     
J- Type thermocouple sensors (at least one pair for measuring one pole)MAX31855
interface chipAt least one pair of MAX31855
interface chip for measuring one pole. (Vcc= -3V to 4V)Arduino
UnoA microcontroller based on ATmega328P. 4 Arduino Software (IDE)This software is to be used to burn the required code into the specified
microcontroller. Here, Version 1.6.12 is being used.  7.
Work schedule (month wise)

(a) Jan 2018

The major action
plan in January is to identify the problem being faced and draft several
versions of possible logical solutions. Once the course is finalized,
identification of the proper sensors to be used, and a thorough market study is
to be done. And once that is done, interfacing the sensors with the
microcontroller is to be begun.

 

(b) Feb 2018

Thorough test runs
of the interfacing is to be done. If it is not successful, other options are to
be looked out for before mid-February. And once interfacing is successful,
start working on calculation of temperature rise.

 

(c) Mar 2018

Once the temperature
rise calculations are through with, add a typical buzzer sound for product
failure notification.

 

(d) Apr 2018

A typical buzzer
sound for product success notification is to be programmed. Once that is done,
the other different clauses for successes mentioned in the standards are to be
worked on.

 

(e) May 2018

Discussions
regarding the future scope of this project, and how they are to be implemented
have to be done.