Why is PLC so reliable? This is not a simple question, you have to answer, not one or two articles. Here, only the experience of the STIPLC chief engineer has exchanged with friends: 1. What is the content of the content? Reliability means that the product can accurately complete all the functions designed under the specified conditions. Electronic products generally include: (1) Mechanical performance (2) Electrical performance (3) thermal performance (4) Chemical performance (5) Biological performance (6) reliability aspects, as long as it is all in these aspects The implementation of careful scientific implementation, the product is reliable. Mechanical properties: mainly considering the reliability of connecting under various conditions, such as vibration, impact, falling, cold and cold, corrosion, mold, dust. There is also the electrical intensity, flowing capacity, and lifting life of the mechanical interface. Important should be redundant (a telecommunications session). Within the vibration frequency range specified by the test standard, it is best no resonance point. If so, it should be ensured that the connection is reliable. Thermal performance: mainly considering the thermal design of the power components, considering the worst case, the junction temperature of the power components is below the allowable value. This should be familiar with heat transfer. In addition, the drive edge of the power component is shaking and reduces switching power consumption. Pay attention to the parameters of the components within the temperature range specified in the product, there is enough balance. Eliminate the warm drift from the design of precision detection. Chemical performance: To process depending on possible, such as acid base, salt fog (such as sea radle, port). Biological properties: For humid high temperature occasions (such as sea-wheels), mold erosion is common, some materials used should meet standards (such as marine standards), and induced. Use performance: When you use user error (such as getting wrong, reverse), not bad as possible. Electrical performance: (1) To meet basic properties: electrical strength (withstand voltage), insulation resistance, voltage fluctuation (such as 25% - 30%), frequency fluctuations. Pay attention to the PCB wiring, and the internal wiring crawling distance (high humidity), internal cable, and PCB printing lines. (2) Special attention to the design of the power supply: The capacity is sufficient (under high temperature full load), the load is very heavy and the small capacity is good, and the dynamic static is good, and the electricity is unblocked (or a small amount). Soft started), it is necessary to resist the instantaneous interruption of the grid voltage (if you can maintain a 240 millisecond power supply), it is resistant to filter surge voltages, electric fast pulse groups, and other modes and differential mode interference and destruction. There is also overloaded short-circuit protection capabilities. (3) The ground design is extremely important, and the principle of a point will always remember. Large current and small current, simulation and numbers, strong power and weak electricity (must be partially regions). It can also be a point in common land. (4) The drive sensitive load should be bounce, do not drive directly with a trigger or latch. Inspective and negative plants are continued. (5) Do not power the logic circuit for large current load. When the total power supply is pulled down when the large current load action is pulled, other circuits are powered normally.
(6) The output is adopted: password refresh, 3 to take 2. (7) Input adoption: filter, 3 to take 2. (8) minimize input (from anti-interference angle) impedance, output impedance (9), if there are multiple power supplies, design is asynchronous to power off. If you can't do it, you should make sure the MOS power is powered down. (10) High-power components should pay attention to DV / DT, DI / DT, and switch loss (11) The input and output ports must be discharged to prevent static. (12) There is often such a situation: When this device is electrocurable, other devices connected to its input and output are electrically, and should be paid attention to protection (especially MOS). (13) Input is often designed with filtering circuits, but pay attention to the logic of transient logic after power-on and the logic of no input signals, which is not paying attention to it. (14) Output circuitry should ensure that malfunction will not occur during power-on and power-off. (15) The reset of the processor CPU should be present later than the input reset time, but the output reset time is later than the CPU power-on reset time, and is higher than the CPU power-down. (16) In order to prevent the CPU from being output due to the interference, the CPU is less than the output delay due to the time of the watchdog, and the output is timely correction and misunderstandings. (17) Serial Communication To add an error-in-error (18) network control system, the operational output must not be performed before the full valid input signal is not received. (19) Weak signals Try to use Differential Input Output (20) Longline Interface to Dwelling Incident and Electrostatic Protection (21) The external circuit of the board or module is isolated between the bus mothernel, and the power supply of the external circuit is best. External power supply (do not use DC / DCs with transformers to supply power by the motherboard), so that when a plate or module is inserted, it is destroyed by the user. (22) In order to prevent radiation and magnetic field interference, the closure area is prevented from forming a closed loop during wiring, and the closed-loop area when the non-closed loop is as small as possible. (23) In order to prevent common mode interference and electrostatic discharge interference, pay attention to reasonable grounding and floating land. The principle is that there is no interference current or voltage to be applied to the internal circuit components. (24) Components To decrease design (electrical parameters and thermal parameters) (25) Note that the consequences and design of the components failure will have a variety of possible external equipment failure consequences. (26) The necessary redundant design (27) The command in serial communication uses a password opening / password, and cannot use a simple 1/0 (28) to send it to send it to send, unchanged (to reduce communication) Quantity), this is likely that the recipient has not come and receive, and it must have a response and retransmission mechanism when it is like this. It is best to send regularly regardless of the constant. (29) It is best not to communicate with the master-slave mode, should be used in the case of noord or multi-master or the whole host. Because of the mainstay, communication is invalid when the master is faulty.
(30) Bus network should pay attention to monitoring node machine failure and automatically and bus out (31) network must have strong toughness, and any node's power-on-hand-swappable, all affect network operation (32) The input signal line is short-circuit, and it should be detected, and the result is full, and it is not possible to float. 2. Implementation of reliability design (1) The mechanism to affect reliability, solve the problem, the principle and method (2) should be Thoughtful, as far as possible, the drip water can not legene (3) to have a qualitative division, more to quantify (4) Strictly comply with standard and appropriate super standard design (5) Eat penetrate each component usage, read through its data sheet (6) Widening a deep knowledge (7) more accumulation, multi-practice (8) seeking fine: http://blog.21ic.com/more.asp? Name = yzy1102 & id = 16742
