# Feel really stupid. Need help. Thermal switch design problem.

• konto77
In summary, the problem involves two rigid plates with two steel plates and one aluminum plate in between. When the temperature increases, the aluminum will buckle and touch one of the steel plates to close the circuit. The critical axial compressive load equation is used to find the required dimensions of the aluminum plate. The length of the aluminum and steel straps will remain equal due to the rigid end pieces. The problem states to hold the width and thickness of the steel and aluminum constant while solving for the thickness of the aluminum at a temperature of 100 degrees Fahrenheit. The equations to use are alpha*deltaT*L + Pa*L/(Ea*Aa) = xa, Ps = -0.5*Pa, and Pa = Pcr = -4
konto77

## Homework Statement

There are two rigid plates on the ends.

In between them are two steel plates and one aluminum plate. The aluminum one is in the center. When the temperature increases enough the aluminum will buckle and touch one of the steel plates to close the circuit.

alpha(alum) = 12.5 (10^-6) /degF
alpha(steel) = 6.6 (10^-6) /degF

E(al) = 10,000 ksi
E(s) = 30,000 ksi

t(a) = 1/16 in w(a) = 1/4 in These are thickness and width
t(a)<w(a) or else the aluminum will not buckle towards the steel

t(s) = 1/16 in w(s) = 1/8 in

Length = 4 in

With these conditions the aluminum buckles at 180 deg F

Find dimensions that will allow the circuit to close at 100 deg F

## Homework Equations

critical axial compressive load: P(cr) = 4 pi^2 E I/L^2

I = w(a)t(a)^3/12

alpha*deltaT*L + PL/E/A = 0 when there are rigid plates right?

and the problem also says "As the temperature increases, teh lengths of both aluminum and stell straps remain equal because of teh rigid end pieces." Does this mean that length of stell and aluminum will change and remain equal? Or that their change in length equals 0.

## The Attempt at a Solution

I used this equation
alpha*deltaT*L + PL/E/A = 0

with
this equation to get the square root of a negative number for thickness of a
P(cr) = 4 pi^2 E I/L^2

konto77 said:
Does this mean the length of stell [sic] and aluminum will change and remain equal?

konto77: Yes, that is correct. The change in length of the aluminum and steel does not equal zero.
konto77 said:
alpha*deltaT*L + P*L/(E*A) = 0 when there are rigid plates, right?

Incorrect. The right-hand side should be displacement, x, not zero. It should be xa for aluminum, or xs for steel.

Does the problem say anything like, hold ws, ts, and wa constant? I think it perhaps should (or could). And let the unknown for the second part of the problem be ta.

Hint 1: alphaa*deltaT*L + Pa*L/(Ea*Aa) = xa.
Hint 2: Ps = -0.5*Pa.
Hint 3: Pa = Pcr = -4*Ea*Ia*(pi/L)^2.

Keep trying.

## 1. What is a thermal switch and what does it do?

A thermal switch is a type of temperature-sensitive device that is designed to open or close an electrical circuit at a specific temperature. It is commonly used in electrical and electronic systems to protect against overheating and to control temperature levels.

## 2. How does a thermal switch work?

A thermal switch works by using a bimetallic strip or a thermocouple to sense changes in temperature. When the temperature reaches a pre-set level, the strip or thermocouple will bend or produce a voltage, causing the switch to open or close the circuit.

## 3. What are the common problems with thermal switch design?

The most common problems with thermal switch design include inaccurate temperature settings, improper placement or installation, and corrosion or wear on the sensor components. These issues can lead to malfunctioning or unreliable switches.

## 4. How can I troubleshoot a thermal switch problem?

If you are experiencing issues with your thermal switch, first check the temperature setting and make sure it is appropriate for your system. Then, check for any physical damage or corrosion on the switch components. If the problem persists, it may be necessary to replace the switch with a new one.

## 5. Are there any alternative solutions to using a thermal switch?

Yes, there are alternative solutions to using a thermal switch, such as using a thermostat or a solid-state relay. These options may be more reliable and accurate in controlling temperature levels, but they may also be more expensive. It ultimately depends on the specific needs and requirements of your system.

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