Basic knowledge and application field of relay
1. Foundation of time relay
A time relay is a relay that produces electrical close or electrical connection when an electrical or mechanical input signal is given at a predetermined time.
The common functions of the time relay are:
A: power delay (On-delay Operation)
F: power off delay (Off-delay Operation)
Y: star delta delay (Star/Delta Operation)
C: With inst. Contact On-delay Operation with transient output
G: interval delay (Interval-delay Operation)
R: the reciprocating delay (On-off repetitive delay Operation)
K: signal disconnection delay (Off-signal delay Operation)
1. Control power supply
The power terminals between the time relays can generally withstand the external surge voltage of 1500V. If surge voltage exceeds this value, surge absorptive devices must be used to prevent the time relay from burning down.
When the time relay works repeatedly, the time when the power is turned off to the next power supply is longer than the reset time. Otherwise, the time of the incomplete reset will delay, time offset, instantaneous or no action during the next time.
The power on time delay relay must be longer than 0.5 seconds, so that there will be enough energy reserves to ensure that the load is switched on or off at preset time after the power is disconnected.
The power supply circuit in general time relay is a high impedance, therefore, cut off the leakage current after the power to be as small as possible (with RC and semiconductor or connected to the contact switch, a time relay) to avoid induction voltage and false shutdown caused by misoperation (for short time delay type, the delay time will generate electricity after that but does not relay release phenomenon). In general, the residual voltage of the power terminal should be less than 20% of the rated voltage, and it should be less than 7% of the rated voltage for the time delay type.
When the time relay completes its control work, try to avoid the continuous electricity. When continuous electricity makes the product heat, thus speeding up the aging of electronic components, greatly shorten the service life.
2. Load connection
Because the output contacts of the time relay are limited by the volume of the products, they often have poor load capacity. Therefore, the contacts should be protected, and they can be connected to the absorption devices at the ends of contacts (such as RC, diodes, zener diodes, etc.).
Do not use time relay to directly control the large capacity load. Some of the loads do not seem to be very large, but the phenomenon of burning contacts occurs due to the load current characteristics. The following table is the relationship between the load form and the surge current.
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