Ten Daily Electronic Common Sense-Section 45

What is the main component of parallel parasitic capacitance?

The parallel parasitic capacitance is mainly composed of the inherent capacitance of the coil and the distributed capacitance of the cable.

When considering installing a WirelessHART network, what are the recommendations that are very important?

1. For security reasons, in the WirelessHART network, the device information must be pre-configured to the network manager. This information will be used to check security and authentication as the device joins the network. The join key is necessary to decrypt the payload of the join network request message. For security, each device should have a different join key. Thus, the network manager must also store the device IDs and device long labels of network devices. The join network request message also includes the device ID and the device long label of the network device. Device IDs are unique for all HART devices. However, when we replace a failed device, using the device ID to authenticate the device creates some extra work for the network manager.
2. When the network manager configures a unicast link between two devices, the sender should not send any packets until the receiving link is configured to the receiver.
3. The device ID can be pre-recorded in the network manager together with the network access key and the network ID. It is safer to install the specified device in the specified location, but this may cause some problems with device installation and replacement. For example, how does an engineer know where a piece of equipment should be installed? So what really matters is getting the right type of equipment in the right place. The device’s label may identify the device’s physical location. We can have the network manager record the device’s label before it joins the network, so the network manager can know the physical location of the device. To assist in the installation of the device, the handheld device must be able to configure the network key to the field device.
4. WirelessHART networks require devices to have highly accurate clocks to keep time synchronization. However, not all devices meet the requirements in this regard. Therefore, the network manager should set a short keep-alive interval for these devices.
5. Pairs of deployment access points can provide better redundancy, the specific reasons have been described.
6. Although the deployment of the WirelessHART network does not require site surveys, site surveys are beneficial and harmless. For example, we can find the most suitable location to install routing equipment through a site survey, so that we can get the strongest signal strength and the least routing equipment.
7. If no new device wants to join the network, the field device can stop sending advertisement messages. This avoids exposure of absolute slot counts and other network information to hostile packet grabbers.
8. Each device has its own join network link. A network link of two adjacent devices can share the same time slot on different physical frequency bands. The network manager should avoid this situation when configuring the link, because in this case the new device will not know who to choose to join the network link.

What is the principle of PWM?

The principle of PWM is that when the input voltage, internal parameters and external loads change, the control circuit performs closed-loop feedback through the difference between the controlled signal and the reference signal. Adjust the on-pulse width of the switching device inside the integrated circuit to stabilize the output voltage or current and other controlled signals.

What is carbon nanotubes?

As has happened in the battery field, capacitors are considered to be a potential application area for carbon nanotubes (CNTs).
Carbon nanotubes are obtained by the catalytic decomposition of hydrocarbons. Depending on the synthesis parameters, single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MW(NTs) can be synthesized, both of which have high accessible surface area and high electrical conductivity. However, the capacitance of pure carbon nanotubes The value is not high, only 20～80F/g. This is mainly due to the small pore volume of carbon nanotubes.
In MWCNTs, the micro-cell volume can be increased by activation. However, compared to activated carbon capacitors, the capacitance value is still low. Surface functionalization by introducing pseudocapacitance through oxidation treatment can greatly increase the capacitance value in protonated solvent media, however, the cycle life is limited in this case.
Currently, much research has focused on how to develop dense, nano-ordered, and vertically oriented carbon nanotube arrays with current collectors. Such carbon nanotubes can fine-tune the tube spacing, thereby increasing the capacitance. Such a carbon nanotube-based nanostructured electrode is very promising, especially in the field of microelectronics.

What is an illegal address (ILAD) reset?

Internal reset due to an access to an illegal address outside the addressing range while reading an opcode. But when storing data, accessing an illegal address will not generate a reset.

What is a power MOSFET?

We all know how to use diodes to switch, but we can only switch them, not gradually control the flow of signals.
Also, diodes act as switches depending on the direction of signal flow; we cannot program them to pass or block a signal. For applications such as “flow control” or programmable switches, we need a three-terminal device and a bipolar transistor. We’ve all heard of Bardeen & Brattain, who invented the triode by accident, like many other great discoveries.
Structurally, it is implemented by two back-to-back junctions (not a big deal, we probably implemented the common cathode with the same structure long before Bardeen). However, functionally it is a completely different device, like a “faucet” that controls the flow of emitter current – the “hand” that operates the faucet is the base current.
Bipolar transistors are therefore current-controlled devices. Field effect transistors (FETs), although structurally different, provide the same “faucet” function.
The difference is this: FETs are voltage controlled devices; you don’t need base current, you use voltage to implement current control. The bipolar transistor was born in 1947, not long after the brilliant father and son Shockley and Pearson invented (at least in concept) the FET.
In order to distinguish it from the earlier bipolar “twin brothers”, the three electrodes of the FET are called drain, gate and source respectively, and the three electrodes of the corresponding triode are the collector, base and emitter. pole.
There are two main variants of FETs, which are optimized for different types of applications. JFETs (junction FETs) are used for small signal processing, while MOSFETs (metal oxide semiconductor FETs) are mainly used for linear or switching power supply applications.

What is the role of the state machine?

The state machine is used to control a certain part of the circuit and complete a certain circuit design with a logical sequence or timing law.

What is the terminology of thermistors?

Rated zero-power resistance R25 zero-power resistance means that when the PTC thermistor value is measured at a certain temperature, the power consumption added to the PTC thermistor is extremely low, as low as the power consumption of the PTC thermistor caused by its power consumption. The resistance change can be ignored.
The rated zero-power resistance refers to the zero-power resistance value measured at an ambient temperature of 25°C. The minimum resistance Rmin refers to the minimum zero-power resistance value that a PTC thermistor can have. Curie temperature Tc is for the application of PTC thermistor , the temperature at which the resistance value begins to increase steeply is important. We define it as the Curie temperature.
The resistance of the PTC thermistor corresponding to the Curie temperature RTc=2*Rmin. The temperature coefficient of the temperature coefficient αPTC thermistor is defined as the relative change of the resistance caused by the temperature change. The larger the temperature coefficient, the greater the temperature coefficient of the PTC thermistor. The more sensitive the response is. α=(lgR2-lgR1)/lge(T2-T1) The surface temperature Tsurf means that when the PTC thermistor is under the specified voltage and in thermal equilibrium with the surrounding environment for a long time, the PTC thermal The temperature of the varistor surface.
The operating current Ik is the current flowing through the PTC thermistor, which is enough to make the self-heating temperature rise of the PTC thermistor exceed the Curie temperature. Such a current is called the operating current. The minimum value of the operating current is called the minimum operating current.
Action time ts Under the condition of 25 ℃ environment, add an initial current to the PTC thermistor (guaranteed to be the operating current), and the time elapsed when the current through the PTC thermistor decreases to 50% of the initial current is the action time.
The non-operating current INk is the current flowing through the PTC thermistor, which is not enough to make the self-heating temperature rise of the PTC thermistor exceed the Curie temperature. Such a current is called the non-operating current. The maximum value of the non-operating current is called the maximum non-operating current. .The maximum current Imax refers to the highest current withstand capability of the PTC thermistor. When the maximum current is exceeded, the PTC thermistor will fail.
The residual current Ir is the current in the thermal equilibrium state under the maximum working voltage Vmax. The maximum working voltage Vmax The maximum working voltage refers to the highest voltage that is allowed to continuously maintain the PTC thermistor under the specified ambient temperature.
For the same product, the higher the ambient temperature, the lower the maximum working voltage. The rated voltage VN The rated voltage is the power supply voltage below the maximum working voltage Vmax. Usually Vmax=VN 15% breakdown voltage VD breakdown voltage refers to PTC The highest voltage withstand capability of the thermistor. The PTC thermistor will fail when it is above the breakdown voltage.

What is magnetic permeability?

• Magnetic permeability—-Also known as magnetic permeability coefficient, is a coefficient to measure the magnetic permeability of a substance, expressed by the letter μ, and the unit is henry/meter.
• Hysteresis—-In the process of repeated magnetization of a ferromagnet, the change of its magnetic induction always lags behind its magnetic field strength. This phenomenon is called hysteresis.

How to configure in the passive mode of FPGA?

In passive mode, the configuration process is initiated and controlled by other devices in the system. These devices can be Altera’s configuration chips (EPC series), or intelligent devices such as microprocessors and CPLDs on a single board. The FPGA is completely passive during the configuration process, and only outputs some status signals to cooperate with the configuration process.