In the past two decades, the electronics industry has developed at an
alarming rate. Ambient temperature conditions will produce the same results.
The application of wirewound resistors in precision circuits will be
discussed in the following technology comparison. With the popularity of
applications, chip resistors play an increasingly important role. Their space
utilization is better than discrete packaged resistors, reducing the amount of
pre-assembly preparation work. Each component in the system has inherent
advantages and disadvantages related to overall performance, especially issues
such as short- and long-term stability, frequency response, and noise. The
discrete resistor industry has made advances in wirewound, thick film, thin
film, and metal foil resistor technologies, each of which has many tradeoffs in
terms of cost per unit of performance. Advances in new technologies, while
reducing device size, have also increased pressure on discrete component
manufacturers to develop devices with ideal performance.
Although upgrading each component or subsystem can improve overall
performance, overall performance is still determined by shortcomings in the
component chain. Therefore, an ideal resistive element should be able to balance
itself according to these natural phenomena, maintain physical consistency
during the resistor processing process, and do not need to compensate for
thermal effects or stress effects during use, thereby improving system
stability.
When electric current passes through a resistive element, it generates
heat, and the thermal reaction causes mechanical changes in the expansion or
contraction of each material in the device. Note, however, that wirewound
resistors are not available in chip versions, so applications requiring
precision chip resistors due to weight and size constraints do not use them.
When the shape, length, geometry, configuration or modular structure changes due
to mechanical or other factors, the electrical parameters will also change. This
change can be expressed by the basic equation: R=ρL/A, where
R = resistance value in ohms,
ρ = material resistivity in ohm meters,
L=length of resistive element, in meters,
A=cross-sectional area of resistive element, in square meters.
Among these devices, chip resistors currently remain in high demand and are
the basic building blocks of many circuits. The main parameters include ESD
protection, thermal electromotive force (EMF), thermal coefficient of resistance
(TCR), self-heating, long-term stability, power coefficient and noise, etc.
Stress, whether mechanical or thermal, causes changes in the electrical
parameters of a resistor.
Precision wirewound resistor
Wirewound resistors are generally divided into power wirewound resistors
and precision wirewound resistors. This process produces permanent deformation
as opposed to elastic deformation or reversible deformation, and the resistance
wire must be annealed. Both methods will change the resistance with or without
power.
The initial error of wirewound resistors can be as low as ±0.005%.
Permanent mechanical changes (unpredictable) can cause arbitrary changes in the
electrical parameters of resistance wires and resistors.
It is difficult to guarantee precise consistency between two wirewound
resistors with the same rated resistance value over a specific temperature
range, and it is even more difficult when the resistance values are different,
or the sizes are different (for example, to meet different power requirements).
Moreover, the resistance core and the number of turns per inch are also
different, and the mechanical properties have different effects on the
electrical properties.
Because of the coil structure, the wirewound resistor becomes an inductor,
and inter-coil capacitance develops near the number of turns. In order to
improve the response speed during use, special processes can be used to reduce
the inductance. Since different resistance values have different thermal engine
characteristics, their operating stability is not the same, and the designed
resistance ratio will change greatly during the device life cycle. However,
lower the resistance value, wirewound resistors are generally 15ppm/°C to
25ppm/°C. Therefore, this discussion does not consider this resistance. Taking
the example of a 1-kΩ resistor versus a 100-kΩ resistor, this inconsistency is
due to differences in diameter, length, and possibly the alloy used in the
resistance wire. In the long term, wirewound components undergo physical changes
as the resistance wire adjusts to its new shape. TCR characteristics and ratios
are extremely important for high-precision circuits. This difficulty is further
exacerbated as the difference in resistor values increases. Different wire
diameters, lengths and alloy materials can achieve the required resistance and
initial characteristics.
Traditional wirewound resistor processing methods cannot eliminate the
various stresses generated during the winding, packaging, insertion and lead
forming processes.
Wirewound resistors are generally made by wrapping insulated resistance
wire around a spool of specific diameter.
During the processing of wirewound resistors, the inner surface of the
resistance wire (the side closest to the spool) shrinks, while the outer surface
stretches. Therefore, there is great uncertainty in the electrical performance
parameters of resistive elements. Power wirewound resistors will undergo great
changes during use and are not suitable for use in situations where high
precision requirements are required. Due to the inductance and capacitance
present in the design, wirewound resistors have poor high-frequency
characteristics, especially at frequencies above 50kHz. Wirewound resistors also
have the characteristics of low TCR and high stability. During the fixation
process, the axial leads are often tightened and encapsulated by mechanical
pressure.
Thermal noise is reduced, and TCR can reach ±2ppm/°C within a limited
temperature range. Precision wirewound resistors have higher ESD stability and
lower noise than thin film or thick film resistors. TCR (change in resistance
per one degree Celsius temperature change) can reach a typical value of 3ppm/°C.
However, this increases cost and has limited effectiveness in reducing
inductance.
Thin film resistor
Thin film resistors are made of ceramic substrates with a thickness of 50?
To 250? Composed of metal deposition layers (using vacuum or sputtering
processes). The stability of thin film resistors is affected by temperature
rise.
Due to the small amount of metal, thin film resistors are prone to
self-corrosion in humid conditions. Thin film resistors are more economical and
space-saving when high resistance values are required but accuracy requirements
are moderate. The aging process for sheet resistor stability varies with the
film thickness required to achieve different resistance values and is therefore
variable over the entire resistance range.
They have an optimal temperature-sensitive deposited layer thickness, but
the resistance values produced by the optimal film thickness severely limit the
range of possible resistance values. In addition, changing the optimal film
thickness can seriously affect TCR. Is the resistance per unit area of a thin
film resistor higher than that of a wirewound resistor or BulkMetal? Metal foil
resistors, and cheaper. Because thinner deposited layers are more susceptible to
oxidation, high value sheet resistors have a very high rate of degradation.
Changing the optimal film thickness can seriously affect TCR. This
chemical/mechanical aging also includes high temperature oxidation of the
resistance alloy. Therefore, different resistance value ranges can be achieved
using various deposited layer thicknesses. Because thinner deposited layers are
more susceptible to oxidation, high value sheet resistors have a very high rate
of degradation. During the immersion encapsulation process, water vapor can
introduce impurities, and the resulting chemical corrosion can cause the thin
film resistor to open circuit within a few hours in low-voltage DC
applications.
thick film resistor
As mentioned before, due to size, volume and weight, it is impossible to
use chip type wirewound resistors. These contacts form a complete resistance,
but thermal strains during operation can break the contact. For a given size,
the higher the resistance, the less metal, the higher the noise, and the less
stable it is.
Granular structures also cause thick film resistors to be very noisy due to
the movement of strings of charges within the structure. Since they are
connected in parallel in most cases, thick film resistors will not open circuit,
but their resistance will continue to increase with time and temperature.
Although less accurate than wirewound resistors, thick film resistors are widely
used due to their higher resistor density (high resistance/small size) and lower
cost.
Thick film resistors rely on contact between particles in a glass matrix to
form resistance. Although less accurate than other technologies, we discuss
thick film resistor technology here because of its widespread use in nearly
every kind of circuit, including parts of high-precision circuits where accuracy
is not critical. Therefore, thick film resistors suffer from poor stability
(time, temperature, and power) compared to other resistor technologies. The
glass component in the thick film resistor structure forms a glass phase
protective layer during the resistor processing process, so the moisture
resistance of the thick film resistor is higher than that of the thin film
resistor. Like thin film and metal foil resistors, thick film resistors have a
fast frequency response, but they are the noisiest of the resistor technologies
currently in use.
Metal Foil Resistors
It is very important for resistance molding to apply special metal foils
with known and controllable properties on special ceramic substrates to form
thermomechanical balancing forces.
Maximum capacitance is 0.05pF. The rise time depends on the resistor value,
but the higher and lower resistor values only drop slightly relative to the
middle value. Then, the resistor circuit is photoetched using an ultra-precision
process.
What is a blue and white adjustable resistor and how to wire it?
The use of blue and white adjustable resistors is also relatively
widespread in the electronic components market, but we should pay attention to
how to adjust and connect the blue and white adjustable resistors. How to
connect the blue and white adjustable resistor during use is what we, as
relevant personnel, must understand, as well as its specific usage
characteristics. Today, the editor will briefly describe the main connection
methods for you. The details are as follows:
How to connect blue and white adjustable resistor
1. When welding resistors, the soldering iron should not stay on for too
long;
2. The resistor should be measured and checked before installation;
3. When assembling electronic instruments, if non-color ring resistors are
used, the nominal value marks of the resistors should be facing upward, and the
marks should be in the same order, which is convenient for observation;
4. In order to improve the reliability of the equipment and extend its
service life, the rated power should be 1.5-2 times greater than the actual
power consumption;
5. Select the resistor model and error level according to the technical
indicators of the electronic equipment and the specific requirements of the
circuit;
6. If a series or parallel resistor is needed in a circuit to obtain the
required resistance, its rated power should be considered. When resistors with
the same resistance are connected in series or parallel, the rated power is
equal to the sum of the rated powers of each resistor; when resistors with
different resistances are connected in series, the rated power depends on the
high-resistance resistor. When connected in parallel, it depends on the low
value resistor and requires calculation before application.
General parameters of blue and white adjustable resistors
1. Resistance value: indicates the size of the resistance, such as 47Ω,
220KΩ, 4.7MΩ.
2. Working voltage: Indicates the rated workpiece voltage of this
component. For example: 16V, 25V, 35V, 50V, 100V
3. Error: Indicates the resistance error range, such as ±1%, ±5%, ±20%.
We have briefly introduced the meaning and parameters of the blue and white
adjustable resistor in previous news content. Its specifications, parameters and
precautions are what we need to know when connecting the blue and white
adjustable resistor, so that we can The quality must be the best to avoid
unnecessary failures during the production process.
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