Application of solid state relay
Application of solid state relay
HSR series of solid state relay, can be widely used in: computer peripheral interface unit, a thermostat and electric resistance furnace control, ac motor control, intermediate relay and electromagnetic valve control, copy machine and fully automatic washing machine control, signal lights and scintillator control, lighting and stage lighting control, remote control system of CNC machine, automatic fire protection and security systems, high power thyristor trigger and industrial automation devices, etc.The following issues need to be considered in the application.
1. Heating of devices
When SSR conducts, the element will bear some heat dissipation power with P consumption =V, where the effective values of V and I are the effective values of saturation voltage drop and working current respectively.At this time, based on the actual work environment conditions, strict adherence to the rated working current allow shell temperature (75 ℃), the reasonable choice radiator size or reduce the current use, otherwise will cause out of control due to overheating, even cause damage of product.
For continuous load current of 23A, S?3 s euro?4. For 5A products, S?08W3 packaging products.Below 10A, the instrument bottom plate with good heat dissipation condition can be used.Above 10A, need to match radiator.Natural air cooling is adopted below 30A. When continuous load current is greater than 30A, forced air cooling by instrument fan is required.
2. Packaging and installation forms
Horizontal W type, vertical L type, small size suitable for PCB direct welding installation.The vertical L2 type can be used for both soldering and mounting of circuit board.Model K and F, suitable for the installation of radiators and instrument baseplates.When high-power SSR(k-type and f-type package) is installed, it shall be noted that the contact surface of the radiator shall be smooth and coated with heat-conducting silicone grease (pioneer t-50).The larger the mounting torque, the smaller the contact thermal resistance.Cold pressing welding sheet is needed for large current lead wire to reduce the contact resistance of lead wire.
3. Input driver
According to the input control mode, SSR can be divided into resistance type, constant current source and ac input control type.At present, it mainly provides resistance input type for 5VTTL level.When other control voltages are used, current limiting resistors can be selected accordingly.SSR input is a current-type device. When the input optocoupler thyristor is fully on (order of microsecond), the power thyristor is triggered.When the excitation is insufficient or the trigger voltage of inclined wave type, it may cause the power SCR to be at the critical conduction edge, and cause the damage caused by the main load current flowing through the trigger circuit.
For example, basic performance test circuit, input as adjustable voltage source, test load with 100W bulb, input trigger signal should be step logic level, strong trigger mode.Foreign manufacturers to provide the device standard current of 10 ma, considering the whole working temperature range (40 + 70 ℃), luminous efficiency stability and anti-interference ability, recommend the best dc current trigger between 12 to 25 ma.SSR input can be driven in parallel or in series.When used in series, one SSR is considered at 4V voltage, and 12V voltage can drive 3 SSRS.
4. Interference problem
SSR products are also a kind of interference source. When conducting, radiofrequency interference of radiation or power line will be generated through the load. The degree of interference varies with the load.The resistance type of incandescent lamp produces less interference, and the zero-voltage type conducts near the zero-crossing region (i.e., zero voltage) of the ac power supply, so there is less interference.The way to reduce the load is in series inductor coil.In addition, cross interference should be avoided between the signal line and the power line.
5. Overcurrent/overvoltage protection
General over current protection methods for fast fuses and air switches.The quick fuse can be selected according to 1.2 times of rated working current, and the fuse can be selected for general small capacity.Special attention to load short circuit, is the main cause of damage to SSR products.For inductive and capacitive loads, besides internal RC circuit protection, it is recommended to use piezoresisors in parallel at the output end as combined protection.The area size of zinc oxide varistor (MOV) determines the absorption power, and the thickness determines the protection voltage.Ac 220V SSR, selected MYH12, 430V, 12 piezoresisors;380V selected MYH12, 750V varistor;The motor transformer with larger capacity should choose the voltage-sensitive resistor with larger capacity of MYH20 and 24.
6. Load considerations
SSR should not be a problem for general loads, but some special load conditions must be considered to avoid excessive impulse current and overvoltage, which may cause unnecessary damage to device performance.The "cold resistance" characteristics of incandescent lamps and electric furnaces cause instantaneous surge current, several times over the rated working current value.General type SSR can be selected according to 2/3 of the current value.Enhanced SSR can be selected according to the parameters provided by the manufacturer.It is recommended to leave sufficient voltage and current allowance in the industrial control site under adverse conditions.
Some types of lamps have a low impedance when burned out.Gasification and discharge channels and capacitive loads, such as switching capacitor Banks or capacitor power supplies, can cause a similar short-circuit condition.Further series resistance or inductance can be used in the circuit as a current limiting measure.When the motor is turned on and off, it will also generate large impulse current and voltage.Dithering caused by unreliable suction of intermediate relays and solenoid valves, and superposition of capacitor voltage and power supply voltage will generate surge voltage of double power supply at both ends of SSR during commutating of capacitor commutating motor.
When the control transformer is primary, the effect of transient voltage on the secondary line on the primary should also be considered.In addition, it is also possible that the current asymmetry in the two directions may lead to the abnormal phenomenon of inrush current caused by saturation.It is through oscilloscope to measure the possible surge current and voltage, so as to choose the appropriate SSR and protection measures.
Solid state relay has been widely used in computer peripheral interface devices, electric furnace heating thermostatic system, CNC machinery, remote control system, industrial automation devices;Signal lamp, scintillator, lighting stage light control system;Instruments and meters, medical instruments, photocopiers, automatic washing machines;Automatic fire protection, security system, as well as power grid power factor compensation capacitance switch, etc.
