Vtrons Blog

Vtrons Blog

Electronics News

1. SMIC and Brite 40LL dual-core ARM Cortex-A9 tests up to the expected target (2012-06-22) [controller and the processor]
2. ST Ericsson restructuring is completed to strengthen ModAP business profit first (2012-06-21) controller and the processor]
3. Eaton advanced UPS uninterruptible power supply to help build electronic government (2012-06-21)
4. LED lamps enter the Japanese market on July 1, 2012 will implement the PSE certification (2012-06-21) [photoelectric and display]
5. Computex2012 successful conclusion of the Source Division to lead the store a new opportunity (2012-06-21)
6. Smart TV box sky fly, and industry standards to be unified (2012-06-21) [controller and the processor]
7. Kontron board equipment for end-to-end wireless Lufthansa cabin IFE solutions (2012-06-20) [RF & Microwave]
8. Energy Micro start EFM32 Gecko MCU sampling plan (2012-06-20) [MCU]
9. The Huizhou Cloud Expo will be held the first to create the Internet of Things and cloud computing industry (2012-06-20)
10. Chinese officials and communications industry leaders will attend the opening ceremony of Asian Mobile Communications Expo (2012-06-20)

How to select RIGHT Potentiometers

Select a potentiometer for your product, you should not only according to the requirements to select type and size, but also meet the requirements of your products, such as performance and main parameters. So various factors should be considered to choose the right potentiometers. Following are the basic methods for you:

1．Potentiometer type is selected according to the operating requirements

Carbon: In general and low-requirement circuit, or better operating environment, synthetic carbon film potentiometer is the first choice. Carbon potentiometer has advantage of high resolution, wide resistance range, completed sizes and cheap, but it has poor moisture resistance and low reliability, so carbon potentiometer is widely used in household appliances, such as volume potentiometer with switch in transistor radios; Slide carbon potentiometer used in TV for volume adjusting; and high load and other household appliances use carbon potentiometer. Besides, carbon potentiometers has long life, and you can use in the wear and long-life circuit.
Wirewound: If the circuit needs to be precisely adjusted, and high power, you should choose wirewound potentiometers. It has large distribution parameters, and only apply in low-frequency circuits, if high-frequency circuit, wirewound potentiometer is not feasible. Besides, wirewound potentiometers has small noise, and apply in low noise circuit.
Cermet: Cermet potentiometer have wide range of resistance, high reliability, high-frequency characteristics, heat resistance, good moisture resistance, it's the first choice for higher operating frequency circuit and precision electronic equipment; besides, it can be used in small electronic devices.

2. Resistances change according to application

The potentiometer's resistance changing characteristics is selected according to the purpose to use. For example, for volume control, it's better too choose the exponential potentiometer; if non exponential, you can choose linear potentiometer instead, but not logarithmic potentiometer, otherwise it will be smaller the volume section range, for partial pressure, it's better to choose linear potentiometer; and use logarithmic potentiometer for tone control.

3. Potentiometer parameter is selected according to the requirements of the circuit

The parameters of the potentiometer are resistance, rated power, maximum operating voltage, linear accuracy and mechanical life, they are the basic points to select. After selecting the type, it is necessary to select the the potentiometer technology and performance parameters according to the requirements of the circuit.
Different potentiometer has different mechanical life. Normally, carbon film potentiometer has the longest mechanical life, up to 200,000 circles; cermet potentiometer's mechanical test life is only 100-200 circles. You should select right mechanical life potentiometer according to the wear resistance of circuit requirements.

4．Note the requirements of the structure

Selection of potentiometer, pay attention to the size, shaft length and shaft end style handle, as well as the shaft position locking switch, single joint or multi-joint, single turn or multi-turn etc.
For frequent adjustment potentiometer, you should select potentiometer with plane shaft end, in order to install the knob. If not require frequent adjustment, you can choose potentiometer with channel shaft end, in order to adjust with a screwdriver, to maintain the relative stability of the state of work. For accurate and no changes after adjusting circuit, it's better to choose potentiometer with locking device.
For potentiometer with a switch, the switch is main for the circuit power supply on-off control, and potentiometer is for power adjustment. There're some types SPST, SPDT and DPDT, select depends on the requirement. Also switch potentiometers can classify into push-pull switch potentiometer and rotary switch potentiometer. For push-pull switch potentiometer, when the switch act, the moving contact is not working, and the benefits are: no wear to the resistor body wear and not change the position of the potentiometers; For rotary potentiometer, when switch act, moving contact will glide on the resistor body. So the wear will affect the life of the potentiometer.
Single potentiometer is used to adjust the single electricity. For two-channel tape recorders, CD players and other stereo equipment, it should select double potentiometer to adjust volume and tone.
For Sophisticated electronic equipment, automatic control device and computer servo control circuit, all should select multi-turn potentiometer.
Slide potentiometer is normally used in the design of electronic equipment, in order to beautify the layout or to save room.

Knowledage for Trimmer Pots

Cermet Trimming Potentiometer is made by screen printing method in accordance with certain graphics, and coated the substrate by the metal glass ceramic uranium resistance paste, finally shaped by the high temperature sintering.

Features:
Wide range of resistance, good heat resistance, strong overload, good resistance to moisture and wear...Cermit Trimming Potentiometer is a promising protentiometer. But it has a noise when contact resistance and current.

Select and Set Up Points:
1. Please select the Trimming Potentiometer's type and tolerance according to the circuit.
2. In general circuits, we use 10% or even 20% of the carbon film Trimming Potentiometer are good enough.
3. For Rated Power, you'd better choose 1.5-2 times of Actual Power to ensure reliable and durable.
4. Before the Trimming Potentiometers are assembled into the circuit, verify its resistance by ohm gauges.
5. When assembling, make sure the type and resitance are easy to see in order to verify.

Testing method:
1. turn the rotating handle, turn handle to see whether it turns smoothly and the switch is flexible?
2. When swith is on or off, whether the short "clicks" is crisp? and listen to sound between the internal contact and resistance, if any "imperfections" sound, indicating poor quality.
3. Test with a multimeter, choose a right resistance according to the resistance of Trimming Potentiometer, and then go on testing according to the following method.
A. Use the multimeter to test "1", "2" ends, the reading should be the nominal resistance of the Trimming Potentiometer. If the handle of the multimeter doesn't move, it indicates that the potentiometer is damaged.
B. Test the contact between movable arm and resistanceac card. Use multimeter to measure "1", "2" (or "2", "3") ends, move the Trimming Potentiometer shaft counterclockwise to close the "off" position, then the smaller resistance the better. Then turn the shaft clockwise, the resistance value should be increased gradually, the handle of the mutimeter should be a smooth move. When the shaft close to "3" ends, the resistance should be close to the nominal resistance of the Trimming Potentiometer. If the handle of multimeter jumps in the process of rotation, indicating the contact is bad.