One of the most basic, yet often misunderstood, components of a control system is the simple HOA Hand-Off-Auto switch. Undoubtedly there are many installations in which multiple control switches are needed in different areas of the plant in order to control a single field device. And if so, what term should be used if the SCADA system allows plant personnel to manually set a fixed PLC output to control the field device rather than allowing the PLC itself to automatically set the output?
On the other hand, Mode of Control, refers to the control strategy used to operate the device. But in larger and more modern systems in which there are multiple places and means of operating a device, the term HOA is often insufficient. Thus, by distinguishing between these two aspects Location of Control and Mode of Controlwe can determine how to implement a control switch or switches that can accommodate a wider range of modern control systems.
Regardless of what is decided, the most important thing to avoid is having multiple switches with redundant labeling i. Unless a very specific application demands redundant switches or mixed-terminology switches, it is better to avoid them altogether. Consider the following example: A motor has two control switches that control its operation: the first is located in the Motor Control Center MCC and the second is located on a control station directly near the motor.
How are these switches wired to control the motor? Perhaps more importantly, how are plant personnel going to correctly remember and understand the various switch combinations?
Instead, properly understanding Location of Control and Mode of Control can solve the issue. Typically, the control switch at the MCC determines where the motor will be control — thus, this switch would be the Location of Control. Instead, a proper understanding of Location of Control will lead to better design of the control switch. Regardless of your particular installation, recognizing the difference between Location of Control and Mode of Control can alleviate much of the confusion that arises when either multiple control switches are needed or a SCADA interface adds another layer of control situations.
Keeping the terms separate and identifying the true function of the control switch will not only streamline design for the engineer, but also help avoid unnecessary headaches for plant personnel as they operate the system. Please contact us today if you have feedback, questions, or need assistance! Conclusion Regardless of your particular installation, recognizing the difference between Location of Control and Mode of Control can alleviate much of the confusion that arises when either multiple control switches are needed or a SCADA interface adds another layer of control situations.
Another symbol often used to represent this type of switch is shown in Figure 2 — Selector switches often contain multiple contacts and multiple poles Figure 2 — A symbol used to represent a selector switch with three poles, each having three terminals, is shown in Figure 2 — This selector switch contains a common terminal for each of the three poles.
The common terminal is connected to the movable contact. A different type of selector switch is shown in Figure 2 — Switches of this type are often supplied with a chart or truth table indicating connections between contacts when the switch is set in different positions.
In this example, there is no connec- tion between any of the contacts when the switch is set in the OFF position. When the switch is set in position A there is connection between contacts 3 and 4, and 5 and 6.
When the switch is set in position B there is connection between contacts 1 and 2, 5 and 6, and 7 and 8. It is not uncommon to see a combination of selector switches, push buttons, and meters mounted on a single control panel Figure 2 — Your email address will not be published. Sections About. Categories Home Appliance Repair Uncategorized. Posted on December 9, by admin Leave a comment.
Selector Switches Selector switches are operated by turning a knob instead of pushing a button. View all posts. Induction motor:Rotor Torque and Breakdown Torque. Transformer:Separation of Core Losses. Armature reaction and commutation:Load Sharing. Audio Principles:Audio Level Metering. Leave a comment Cancel reply Your email address will not be published.You could be a service technician who wishes to try to find recommendations or address existing troubles.
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Hand Off Auto Switch Wiring Diagram
Tags: hand off auto selector switch wiring diagram hand off auto switch wiring diagram square d hand off auto switch wiring diagram. Toggle navigation. Gravely K Wiring Diagram.Recognize hand-off-automatic switches on a schematic diagram. Hand-off-automatic controls are used to permit an operator to select between automatic or manual operation of a motor.
The switch is shown as a single-pole double- throw switch with a center Off position. Another symbol for a hand-off-automatic switch is shown in Figure 27—2. This switch is shown to contain two separate sets of contacts. One set is labeled and the other is labeled The switch chart indicates that when the switch is in the Off position, there is no connection between any of the contacts.
When set in the Hand position, connection is made between terminals 1 and 2. When set in the Automatic position, connection is made between terminals 3 and 4. This circuit is the control for a large fan that pulls air through a building. Starter M1 controls the fan motor, and starter M2 controls a pump used to circulate water through the motor.
When the hand-off-automatic switch is set in the Hand position, connection is made between terminals 1 and 2. This permits the motor to be controlled by a start-stop push-button station. In this mode, the fan will run continuously until the Stop button is pressed. When the HOA switch is placed in the Auto position, a thermostat controls the action of the fan. A combination push-button station with a hand-off-automatic switch and pilot lamp is shown in Figure 27—3.
The dashed line indicates that the two switches are mechanically connected. When one switch changes position the other switch changes position also. Although the circuit shown in Figure 27—4 looks different than the circuit in Figure 27—2, electrically they are the same and will operate in the same manner.
Review Questions 1. Refer to the circuit shown in Figure 27—2. Would it be possible to replace the hand-off-auto switch in this circuit with a hand-off-auto switch that contained a common terminal and center Off position like the HOA switch shown in Figure 27—1?
Explain your answer. Would the temperature have to increase or decrease to permit the fan to turn on? Which starter controls the holding contacts connected in parallel with the start push button?
Refer to the circuit shown in Figure 27—4.HAND-OFF-AUTO Circuits (Full Lecture)
Assume that the HOA switch is in the Hand position and that the motor is running. Now assume that OL1 opens its contacts. Would this cause the pump motor to stop operating? Now assume that OL2 opens its contacts.The next logical step is to become retail trading desks too.
The point of sale and customer relationship management (CRM) data supermarket chains are constantly gathering is richer than anything any media agency or brand has access to. This data runs both offline and online and brands desperate to better understand their customers would jump at the opportunity to access it. Some global retailers have already been experimenting with this approach, notably Amazon and Walmart, as well as others such as Coles in Australia, but 2016 will be the year the global retail sector really wakes up to the potential of the retail trading desk.
The coming year will see major strides in the aggregation of data from disparate sources into a single view that can be used to drive holistic marketing strategies. Marketers will continue to adopt data management platforms (DMPs) and increase their focus on unifying marketing and advertising data and messaging, resulting in the eventual merger of ad tech and martech.
It will also mean increased collaboration and validated technological partnerships between mid-sized companies looking to make sure their individual solutions can work interoperably towards common marketing goals. The value of third-party data will be further scrutinised as marketers ask, how valuable is data that just about anyone can purchase. And, with the rise of walled gardens, will second-party data become fragmented. To allow advertisers the best opportunity to engage with consumers, first-party data must still rule.
One way we expect brands and agencies to make sure their digital campaigns hit home next year is via an increased focus on moment marketing. Campaigns can be synced to a wide range of events that are likely to impact consumer behaviour, for example a change in the weather, the score of a football match or the screening of a major TV ad campaign.
Everyday changes in the weather are also high on the list of moments that brands want to use to trigger digital campaigns. Other triggers we expect brands to utilise in 2016 include a change in pollution levels. Also that means the money is now going to completely wrong pockets, arguably causing even more damage to the society.
This is highly noticeable with video ads, where poorly managed optimization attempts are causing viewers to wait for several seconds and some times even more until the page fully loads or video content starts playing.
I expect to see substantial improvement in 2016 as video-centric platforms gain better technologies to enhance yield and delivery optimization.
Alternatively, its the year of the video-native-social mobile. To continue reading this article, please exit incognito mode or log in.
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Go to Figma All Collections Live Device Preview Live Device Preview Live Device Preview Our Mirror app lets you view your designs on a mobile device in real-time Written by Jason Updated over a week ago To preview your designs on your mobile device download the Figma Mirror app for iOS or Android here.
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Understanding HOAs to Avoid Confusion for Plant Personnel
Group 65Go to Figma All Collections Live Device Preview Our Mirror app lets you view your designs on a mobile device in real-time Written by Jason Updated over a week ago Did this answer your question. API previews let you try out new APIs and changes to existing API methods before they become part of the official GitHub API. During the preview period, we may change some features based on developer feedback. If we do make changes, we'll announce them on the developer blog without advance notice.
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Migrations Prepare a GitHub repository for migration to GitHub Enterprise. Custom media type: wyandotte-preview Source import Import source repositories to GitHub with the API version of the GitHub Importer. Custom media type: barred-rock-preview Announced: 2016-02-19 Update: 2016-05-03 Enhanced deployments Exercise greater control over deployments with more information and finer granularity.Amanda Risner, United States Iceland Winter World, January 2017 Thor was excellent.
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Motor Starter Wiring Diagrams
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