This same principle can be applied, not only to gain muscular strength, but also to gain flexibility, muscular endurance, and cardiorespiratory endurance.Įach variable can be used independently or in combination with other variables to impose new stress and stimulate adaptation. The lifter will continue to get stronger until his/her maximum capacity has been reached, or the stress stays the same, at which point the lifter’s strength will simply plateau. The lifter adds 20 pounds and continues with the newly established stress of 170 pounds. After 2 weeks of lifting this weight, the lifter notices the 150 pounds feels easier during the lift and afterwards causes less fatigue. As a result of the adaptation, more stress must be applied to the system in order to stimulate improvements, a principle known as the overload principle.įor example, a beginning weightlifter performs squats with 10 repetitions at 150 pounds. As these subsequent adaptations occur, the stress previously experienced during the same activity, feels less stressful in future sessions. ![]() Physical stress, such as walking at a brisk pace or jogging, places increased stress on the regulatory systems that manage increased heart rate and blood pressure, increased energy production, increased breathing, and even increased sweating for temperature regulation. Perhaps a better way to relay the same message would be to say that improvements are driven by stress. If that were true, exercise would be a lot less enjoyable. Using the test button, it is possible to test the control wiring.\)Ĭonsider the old saying, “No pain, no gain.” Does exercise really have to be painful, as this adage implies, to be beneficial? Absolutely not. NC contacts should be capable of direct switching of contactor coil. NO contact is for trip signaling and NC contact is for disconnecting the contactor. They are provided with two auxiliary contacts – one NO (97-98) and another NC (95-96). If the device is set to auto, a remote reset of OLR is possible. With the manual/auto reset selection button, we can choose between manual and automatic reset of these relays after a trip. Reset ButtonĪ reset button is present over the overload relay to reset the overload relay after a trip and clearance of fault. In the case of an electronic overload relay, an additional knob for tripping class selection is also provided. The current can be set between the upper and lower limits provided. Using this knob, the rated current of the motor can be set. Ampere range settingĪ rotary knob is present over the overload relay. Supply to the motor can be connected to Terminals T1, T2, and T3. It can be directly mounted to the contactor. Terminals L1, L2, and 元 are input terminals. Parts of a thermal overload relayĪpart from the bimetallic strip and contacts discussed in the working principle section above, there are a few more parts in an overload relay that needs to be understood. They are designed in such a way to withstand the starting current (which is typically 6 to 10 times the full load current) of the motor for a limited period (typically 15-30 seconds depending on the threshold of current). These measurements can be used for more accurate thermal overload protection. In addition, manufacturers offer built-in RTD or thermocouples that can be directly used to measure the winding temperature. Electronic overload relays are much suited for applications that require a frequent start and stop of motors. Some manufacturers build electronic relays with extensive features such as earth fault protection, motor stall protection, etc. Also, Electronic relays are more precise than thermal relays. The major advantage of electronic OLR over thermal OLR is that lack of bimetallic strip results in low heat losses inside the relay. Some electronic overload relays come with current transformers and Hall effect sensors that directly sense the amount of current flow. Temperature is sensed using PTC and the same is used to trip the circuit in case of overload faults. ![]() It uses microprocessor-based technology for protection. ![]() Instead, it uses temperature sensors or current transformers to sense the amount of current flowing to the motor. Working of electronicĮlectronic overload relays do not have a bimetallic strip inside. The conductor shall be insulated hence no current flow through the strip. Excessive current flow to the motor heats up the conductor and hence the bimetallic strip. Therefore, it gets heated up directly by the current.īut in the case of indirect heating, the bimetallic strip is held in close contact with the current-carrying conductor inside the OLR. In the direct heating method, the full current to the motor flows through the OLR. As explained above, a bimetallic thermal relay works on the heating property of the bimetallic strip.
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