A trimmer in electronics is an adjustable miniature electrical component. It is intended to be set accurately when introduced in some gadget, and never observed or balanced by the gadget's user. Trimmers can be variable capacitors, variable resistors (potentiometers), or inductors. They are commonly used in accuracy hardware like A/V segments and may be balanced when the equipment is serviced. Trimpots are generally used to calibrate electrical equipment initially after manufacturing. Contrary to many other variable controls, these trimmers are clamped on the circuit boards, turned with a little screwdriver, and appraised for several fewer calibration over their lifetime. Trimmers, for example, trimmable capacitors and trimmable inductors are generally found in radio and superhet radio receivers, radio frequency, and intermediate frequency circuits. They are set in the correct position during the time of the alignment procedure of the receiver.

In electronics, Presets are those adjustable components to which the user has no access to. They are made to adjust during the time of the manufacture of that device or during the time of its maintenance/repair. Several passive electrical components can be used as presets, like inductors, resistors, and capacitors.

General Considerations

Trimmers can be found with different levels of precision and sizes. For instance, we have the multi-turn trim potentiometer which reaches its end value after several turns of screw adjustment. This helps in getting a very high accuracy level. Often they also use a leadscrew (linear track) or a worm-gear (rotary track).

Resistors

Resistor trimmers can be found generally in the form of a Potentiometer, often known as trimpot. There are three terminals present in a potentiometer, but it can be modified for a two-terminal resistor by attaching the wiper to any one of the other terminals. Trimpot was patented in 1952 by Marlan Bourns and till then it is a registered trademark of Bourns, Inc.

There are two types of preset resistors that are found in the circuits commonly.

• The first one is the skeleton potentiometer that has the working principle the same as a regular circular potentiometer. The only difference is that it is stripped of its shaft, enclosure, and fixings. The complete movement of this kind of potentiometer is less than a single turn.

• The second one is the multi-turn potentiometer which provides movement to the slider along the resistive track through a worm gear set up. In this potentiometer, the gearing is done in such a manner that multiple turns are required for an adjustment screw to position the slider the complete distance along the resistive track.

This was all we have regarding Trimmer Resistors through hole. We hope that you liked the article. Brands that manufacture them are Bourns, TT Electronics, and Vishay. Make sure to visit them using the links as provided.

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A potentiometer is defined as a 3 terminal resistor having a rotating or sliding contact that makes up the adjustable voltage divider. If you are using only the two terminals present in it (one end and the wiper), then it behaves like a variable resistor or rheostat.

Potentiometer, a measuring instrument, is a voltage divider which is used to measure the electric potential difference. This electric component has got its name as a potentiometer because it is an implementation of the same principle.

Potentiometers are used mainly in controlling electrical devices like in audio equipment for controlling the volume. Potentiometers that are controlled by a mechanism can be utilized as position transducers, like, as used in a joystick. Potentiometers are used very often to control significant power (greater than watt) directly since the dissipated power in the potentiometer is comparable to the power present in the controlled load.

Nomenclature for Potentiometers

There is a vast amount of electronic equipment present in the industry. For the simplification of the people, each of them comes with its code and nomenclature. Let's have a look at the nomenclature as described for a potentiometer.

• Trimmer pot or Trimpot – A trimmer potentiometer is a potentiometer that is generally meant to be calibrated once or infrequently for the electrical signal to get tuned finely.
• Thumbwheel pot or Thumb pot – A rotating potentiometer (small) which can be calibrated infrequently with the help of small thumbwheel.
• Slider pot or Slide Pot – This kind of potentiometer is adjusted with the help of a wiper by shifting it right or left (or even up and down - It depends on the way of its installation), generally with the help of thumb or a finger.

Digital Potentiometer

A digital potentiometer, generally known as digipot, is an electronic equipment that copies all the functionality of analog potentiometers. Just like the analog potentiometer, the resistance present between the 2 terminals can be adjusted through digital input signals.

There are 2 main functional types of digital potentiometers.

• Non-Volatile – It uses a strong mechanism like that present in EEPROM or flash memory to retain their set position.
• Volatile – It loses its set position as soon as the power is removed from them. It is generally designed to initialize at the base position.

The use of digipot is much complex than that of a simple analog potentiometer. Not only that, but there are many noticeable limitations as well. Still, they are broadly utilized, regularly for factory calibration and adjustment of hardware, particularly where the constraints of mechanical potentiometers are dangerous.

Membrane Potentiometers

A membrane potentiometer is a potentiometer that takes the help of a conductive membrane that is distorted by a sliding element to contact a resistor voltage divider. Linearity lies between 0.5 percent to 5 percent as per the designs, materials, and processes used while manufacturing. The repeat accuracy generally lies in the range of 0.1mm to 1.0mm with an infinite resolution theoretically.

This was all we have regarding Potentiometers. Brands that manufacture them are Bourns, Honeywell, and Vishay. Make sure to go through them using the links as provided.

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A thermal cutoff is a safety device for electrical equipment. It ceases the flow of current in a device when heated to a specific temperature. These devices can be reset either automatically or even manually.

Thermal fuse

Thermal fuse is a cutoff that utilizes a fusible link (applicable for only one time). The thermal fuse is not like the thermal switch that gets reset automatically whenever there are temperature drops. On the contrary, it's like an electrical fuse – a one-time-use device that cannot reset itself and needs to be replaced when it is triggered. Thermal fuse is generally used in those situations where overheating is a rare occurrence.

One component is a little meltable pellet that holds down a spring. The spring gets released when the pellet melts completely. As a consequence of this, the circuit breaks up. The NEC Sefuse SF series, Tamura LE series, Hosho Elmwood D series and Microtemp G4A series may manufacture the alloy pellets containing silver, copper, and beryllium to melt at a precise temperature.

Thermal fuses have found its use in heating electrical appliances like hairdryers and coffeemakers. It serves as a safety equipment to cease the flow of current to the device in case of any malfunction that would result in the temperature to ascend to risky levels, potentially lighting a fire. Thermal fuses react only in case of excessive temperature and not during the flow of excess current. This is one of the main differences of the device with a normal electrical fuse. 

Thermal Switch

A thermal switch popularly known as a Thermal Cutout (TCO) or thermal reset is an electrical equipment that opens with a "plink" sound at a higher temperature and closes itself automatically when there is a drop in temperature. The thermal switch is a bimetallic strip that is often encased in a cylindrical glass bulb to shield it from short circuits or dust particles. Another basic configuration utilizes a bimetallic shallow dome-shaped top which "clicks" to an inside out inverted cap when warmed, for example, the "Klixon" brand of thermal cutouts.

The thermal switch can be reused. Thus it is used in temporary places that are user-correctable. Thermal switches are used as thermostats in some cooling and heating system. It is also used in power supplies in case of any malfunction (overload). Another category of thermal switch is the Positive Temperature Coefficient thermistor (PTC). These kinds of thermistors have a “switch” temperature. At this temperature, the resistance rises rapidly and limits the current in the circuit. It is used in motor overheat protection.

Thermal switch is also used in some luminaire, particularly with downlight, where unnecessary heating is well on the way to happen. This might sometime result in "cycling". It is the process where the lights turn on and off after every few minutes. Glimmering radiant Christmas lights take advantage of this impact.

This was all we have about Thermal Cutoffs. Brands that manufacture this equipment are TE Connectivity, Littelfuse and Bourns. Make sure to refer them using the links as provided. Hope you liked the article and Thank you for reading.

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A resettable fuse is a PPTC (Polymeric Positive Temperature Coefficient) device that is a piece of passive electronic equipment utilized in defending against overcurrent faults in electrical circuits. It is also popularly known as polyswitch or a multifuse or a polyfuse. In certain situations, it is noted that this device is much similar to PTC thermistors but instead of charge carrier effects, they are operated on mechanical changes in semiconductors. A PPTC device consists of a voltage rating and a current rating. This electronic device was invented by Gerald Pearson in 1939 at Bell Labs. It was described in US patent #2,258,958.

A PPTC device is manufactured using a crystalline organic polymer matrix which is non-conductive in nature. To make it conductive it is added up with black carbon particle. Several conductive chains of carbons are formed between the crystals when it is cooled. Now as it is good at conducting electricity, the current will pass easily. Passage of a large amount of current through the device will make it heated up. The polymer will expand due to the heating up of the device. As a result, the polymer will change to the amorphous state from its crystalline form. Now as the heat is causing the expansion in the polymer, the carbon particles will start to get separated and the conductive pathways will start to break. As a consequence of this, the device will heat at a much faster rate, expand more and the resistance will be increased. Due to this increase in the resistance the circuital current will decrease. The device still consists of a small amount of current (leakage current) flowing through it which is enough to keep the temperature at a level such that the equipment is at a high resistance state. The range of leakage current is from a few hundred mA at lower voltages to less than a hundred mA at rated voltage. It can be said that latching functionality is one of the characteristic features of the device. 

As soon as the power is removed from the device, the heating caused by the leakage current will cease and the resettable fuse (PPTC) will start to cool down. With the cooling of the device, the original crystalline structure is regained and it gets back to its low resistance state that can hold current. The cooling process of the device generally takes a couple of seconds. 

Resettable fuses are most commonly used in computer power supplies (generally of PC 97 standard), nuclear applications as well as aerospace applications. This device is also used in protecting audio loudspeakers (tweeters). A circuit designed with a PPTC device connected in parallel to the light bulb or a resistor helps in limiting the current through the tweeter to a safer limit. Thus the tweeter will not get damaged if the amplifier is conveying more power that is endurable by it.

This was all we had about Resettable fuses. Brands that make them are TE Connectivity, Littelfuse and Bourns. Make sure to follow them by the links as provided. Thank you for reading up the blog.

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A Gas Discharge Tube or a Gas Plasma Arrestor is an arrangement of gas in an electrode inside a temperature-resistant and an insulating envelope. Gas Discharge Tubes results in the phenomena linked with the electric release in gases and gets initiated by converting the gas into ions with an applied voltage adequate to cause electrical conduction by the basic principle of the Townsend discharge. A gas discharge lamp is an electric light that takes the help of Gas Discharge Tubes; these consist of neon lights, metal-halide lamps, fluorescent lamps, and sodium-vapor lamps. Some specific gas discharge tubes like thyratrons, ignitrons and krytrons support as switching devices.

The required voltage for initiating and sustaining the discharge completely depends on the pressure, the amount of gas-filled in the tube as well as its geometry. Though the envelope is made up of glass, military tubes use glass-lined metal most often while power tubes use ceramics frequently.

As said earlier, the principle mechanism is the Townsend discharge. It is defined as the sustained increase of electron stream by ion impact when a critical estimation of the strength of the electric field for the thickness of the gas achieved. With the increase in the electric field, various discharge phases are encountered. The gas utilized significantly impacts the parameters of the cylinder. The breakdown potential difference relies on the distance between the electrodes and the composition of gas inside the tube.

Gas Used

• Hydrogen – It is used in tubes that require fast switching.
• Deuterium – It is used in neutron generator as well as UV lamps for UltraViolet spectroscopy.
• Noble Gases – It is used for several purposes, from switching to lightning.
• Elemental Vapors – Mercy vapors is used in ignitors, mercury-arc valves etc; Sodium vapors in sodium-vapor lamps; Sulfur vapor in sulfur lamps.

Gas Pressure

The gas pressure is kept between 0.001 and 1,000 Torr. But generally, it is kept between 1 to 10 torr. Factors that affect the gas pressure are as follows:

• Sputtering of cathode – With an increase in pressure, it gets reduced.
• Ignition Voltage or the Breakdown Voltage
• Backfire Voltage
• Operating Voltage
• Current Density
• Lifetime of the tube – Tubes having lower pressure have a short duration of life because of the gas consumption.

Gas Purity

To maintain the desired properties it is important that the gas present inside the tube needs to be kept pure; even a small quantity of impurities can significantly change the values of the tube; the presence of gases that are non-inert results in the increment of burning as well as the breakdown voltage. One can get to know the presence of impurities inside the tube by experiencing the change in the color of the gas glowing. Leakage of air inside the tube results in the introduction of oxygen, which is exceptionally electronegative and represses the generation of electron avalanches. This leads the discharge to look milky, reddish or pale. Traces of mercury vapors gleam pale blue, darkening the original gas shading. To forestall outgassing of the components of the tube during the process, a bake-out is required before loading up the tube with gas and fixing it.

This was a brief idea about the Gas Discharge Tube. We hope that you liked it. Brands that make Gas Discharge Tubes are Bourns, Littelfuse, and EPCOS. Make sure to check them out.

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