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Showing posts with label temperature. Show all posts

Wednesday, November 5, 2014

Pc Temperature Alarm

If your PC overheats, it could damage its expensive components. Here’s a circuit that warns you of your PC getting heated. Today’s computers contain most of the circuitry on just a few chips and reduced power consumption is a byproduct of this LSI and VSLI approach. Some PCs still have power supplies that are capable of supplying around 200W, but few PCs actually consume power to this extent.

On the other hand, apart from some portable and small desktop computers that use the latest micro-power components, most PCs still consume significant amount of power and generate certain amount of heat. The temperature inside the aver-age PC starts to rise well above the ambient temperature soon after it is switched on. Some of the larger integrated circuits become quite hot and if the temperature inside the PC rises too high, these devices may not be able to dissipate heat fast enough. This, in turn, could lead to failure of devices and eventually of the PC. Various means to combat overheating are available, ranging from simple temperature alarms to devices like temperature-activated fans to keep the microprocessor cool.

Here is a temperature alarm that activates an audio ‘beeper’ if the temperature inside the PC exceeds a preset threshold. This temperature is user-adjustable and can be anywhere between 0°C and 100°C. The unit is in the form of a small PC expansion card, which you simply need to plug into any avail-able slot of the host PC. It is powered from the PC and consumes only about 12 mA. The sensor (LM35) used here pro-vides a substantial amount of on-chip signal conditioning, including amplification, level shifting and phase in-version. As a result, it provides an out-put of 10 mV per degree centigrade rise in temperature. It caters to a temperature measurement range of 0°C to 100°C, which corresponds to 0V to 1V of voltage.

Pc Temperature Alarm Circuit Diagram

The voltage-detector stage com-pares the output voltage of the temperature sensor with the preset reference voltage. The output of the comparator goes high if the output potential from the sensor exceeds the reference voltage. When this happens, the voltage comparator enables a low-frequency oscillator, which, in turn, activates the audio oscillator. The out-put of the audio oscillator is connected to a loudspeaker (LS1), which sounds a simple ‘beep-beep’ alarm. The reference voltage determines the temperature at which the alarm is activated.

Fig. 1 shows the circuit of the PC temperature alarm and Fig. 2 shows the pin configuration of sensor LM35. IC LM35 (IC1) is an easy-to-use temperature sensor. It is basically a three-terminal device (two supply leads plus the output) that operates over a wide supply range of 4 to 20V. It consumes only 56 µA at 5V and generates insignificant heat.

IC2 is an operational amplifier used here as a voltage comparator. VR1 pro- vides a reference voltage that can be set anywhere from 0V to approximately 1V, which matches the output voltage range of IC1. This reference voltage is applied to the inverting in- put of IC2 and the output of IC1 is coupled to the non-inverting input. Consequently, the output of IC2 is low if the output of IC1 is below the reference voltage, or high if the output of IC1 exceeds the reference voltage.

Pin details of LM35

Pin

The low-frequency oscillator IC3 is a standard 555 astable multivibrator circuit. It is gated via the reset input at pin 4, which holds output pin 3 low when IC3 is gated ‘off’ (when the out-put of IC2 is low). This prevents IC4 from oscillating. IC4 is another 555 astable multivibrator circuit, gated via its reset input. It has an operating frequency of approximately 2.5 kHz. When IC3 is activated, its output pro-vides a square wave of 1 Hz. This is used to trigger IC4, which gives an audio output of 2.5 kHz in bursts. It is connected to loudspeaker LS1 to generate alarm.

The alarm circuit can be fitted into any spare expansion slot of the PC, but be careful to fit it the right way round. Before setting VR1 to a suitable thresh-old temperature, decide what that temperature should be. The technical specification in your computer’s manual might be of help here. If we assume that the room temperature will not normally exceed 25oC, the temperature of the interior of the computer would be up to 35oC. Unless you have good reason to use a different threshold temperature, VR1 should be set for a wiper potential of 350 mV.

Trial-and-error method can be used in the absence of test equipment to enable VR1, but it would be a bit time-consuming. There is a slight complication in that the computer’s outer casing must be at least partially removed to provide access to VR1. Once VR1 has been adjusted, the outer casing must be put back into place so that the interior of the computer can warm up in the normal way. You must therefore al-low time for the temperature inside the computer to rise back to its nor-mal operating level each time VR1 is readjusted.

Thursday, October 16, 2014

Simple IC LM35 Temperature Sensor Characteristics

LM 35 temperature sensor IC is a IC chip production Natioanal Semiconductor which serves to determine the temperature of an object or space in the form of electric scale, or can also be defined as an electronic component that is used to change the temperature changes are accepted in the electrical wholesale changes. LM35 temperature sensor IC temperature change can change a change in voltage at the output. LM35 temperature sensor IC requires +5 volts DC source voltage and DC current consumption of 60 mA in operation. Physical form LM 35 temperature sensor is an IC chip with packaging that varies, in general packaging LM35 temperature sensor is packaged TO-92 as shown in the figure below.

From the picture above it can be seen that the temperature sensor IC LM35 basically have 3 pin that serves as a source of supply voltage of +5 volts DC, as a result of sensing the output pin in the form of a change in the DC voltage and Vout pin to Ground.

IC LM35 temperature sensor characteristics are:

Temperature sensitivity, with linear scaling factor between voltage and temperature 10 mVolt / º C, so it can be calibrated directly in centigrade.
Have the accuracy or the accuracy of the calibration is 0.5 º C at 25 º C.
Has a maximum operating temperature range between -55 º C to +150 º C. Working at a voltage of 4 to 30 volts.
Has current low at less than 60 mA.
Have a low self-heating (low-heating) of less than 0.1 º C in still air.
Has a low output impedance is 0.1 W for 1 mA load.
have Nonlinearities only about ± ¼ º C.

Wednesday, October 8, 2014

latest Temperature Controlled NICD Charger by IC LM311

This circuit is for a temperature controlled constant current battery charger. It works with NICD, NIMH, and other rechargeable cells. The circuit works on the principle that most rechargeable batteries show an increase in temperature when the cells becomes fully charged. Overcharging is one of the main causes of short cell life, hot cells pop their internal seals and vent out electrolyte. As cells dry out, they lose capacity.

Temperature

Theory
The transformer, bridge rectifier, and 1000uF capacitor provide around 22 Volts of DC power to run the rest of the circuit. The 7812 regulator drops this to 12V to run the 311 comparator and 4011 nand gates.

The start switch is pressed to start the charging cycle. This causes the two 4011 nand gates, which are wired as an r-s flip-flop, to go into the charging mode. The Red LED is lit, and the VMOS FET current switch is turned on. Charging current runs though the battery pack. If the battery starts out warmer than the reference temperature, the circuit will not switch into charging mode. Let the pack cool down. When the battery pack reaches a full state of charge, the differential temperature sensor causes the flip-flop to switch off, turning off the VMOS current switch, and lighting the Green LED.

The 7805 voltage regulator is wired as a constant current regulator. This provides a safe maximum charge current for a number of different cell types. The 500 ohm resistor across the VMOS FET sets the trickle charge current which flows through the battery pack after the bulk charging is finished.

The 1N5818 diode prevents the pack from discharging if the AC power is turned off.

The resistor, diode, and capacitor around the start switch cause the circuit to auto-start when power is first applied.

The differential temperature sensor circuit works by presenting two voltages to the input of the 311 comparator. The comparator output switches on or off depending on which input is at a higher voltage than the other. As the thermistors warm up, their resistance drops, lowering the associated comparator input. Since there are two sensors, the room temperature can vary and the circuit will only react to the difference in temperature between the sensors.

Friday, September 19, 2014

Two Wire Temperature Sensor

Circuit diagram :

Two-Wire

Two-Wire Temperature Sensor Circuit Diagram

If an output signal that is directly proportional to the celsius temperature scale is desired, the present circuit, which uses a Type LM45 sensor, offers a good solution. The LM45 sensor is powered by an alternating voltage, while its out-put is a direct voltage.

The supply to the sensor is provided by a sine-wave generator, based on A 1 and A 2 (see diagram). The alternating volt-age is applied to the signal line in the two-core cable via coupling capacitor C 6 .

The sensor contains a volt-age-doubling rectifier formed by D 1 -D 2 -C 1 -C 2 . This network converts the applied alternating voltage into a direct voltage. Resistor R 2 isolates the output from the load capacitance, while choke L 1 couples the output signal of the sensor to the signal line in the cable. Choke L 1 and capacitor C 2 protect the output against the alternating voltage present on the line.

At the other end of the link, network R 3 -L 2 -C 4 forms a low-pass section that prevents the alternating supply voltage from combining with the sensor out-put. Capacitor C 5 prevents a direct current through R 3 , since this would attenuate the temper-ature-dependent voltage.

The output load should have a high resistance, some 100 kΩ or even higher. The circuit draws a current of a few mA.

Monday, September 8, 2014

Two Wire Temperature Sensor

Remote temperature measurements have to be linked by some sort of cable to the relevant test instrument. Normally, this is a three-core cable: one core for the signal and the other two for the supply lines. If the link is required to be a two-core cable, one of the supply lines and the signal line have to be combined. This is possible with, for instance, temperature sensors LM334 and LM335. However, these devices provide an output that is directly proportional to absolute temperature and this is not always a practical proposition. Circuit diagram : Two-Wire Temperature Sensor Circuit Diagram If an output signal that is directly proportional to the celsius temperature scale is desired, the present schema, which uses a Type LM45 sensor, offers a good solution. The LM45 sensor is powered by an alternating voltage, while its out-put is a direct voltage. The supply to the sensor is provided by a sine-wave generator, based on A 1 and A 2 (see diagram). The alternating volt-age is applied to the signal line in the two-core cable via coupling capacitor C 6 . The sensor contains a volt-age-doubling rectifier formed by D 1 -D 2 -C 1 -C 2 . This network converts the applied alternating voltage into a direct voltage. Resistor R 2 isolates the output from the load capacitance, while choke L 1 couples the output signal of the sensor to the signal line in the cable. Choke L 1 and capacitor C 2 protect the output against the alternating voltage present on the line. At the other end of the link, network R 3 -L 2 -C 4 forms a low-pass section that prevents the alternating supply voltage from combining with the sensor out-put. Capacitor C 5 prevents a direct current through R 3 , since this would attenuate the temper-ature-dependent voltage.

The output load should have a high resistance, some 100 kΩ or even higher. The schema draws a current of a few mA.