Saturday, December 25, 2010

CrazyEngineers Forum - Electrical & Electronics Engineering

CrazyEngineers Forum - Electrical & Electronics Engineering

Electrical and Electronics safety tips and best practices

Posted: 24 Dec 2010 01:52 PM PST

Hi fellow CEans. I thought I would start a new topic listing Electrical and Electronics safety tips and best practices for all of us CEans to help add to. The point is to keep Safety First and keep it on our minds every day. We are all worth more Alive. :) At my company we start all our shopfloor meetings with a saftey tip from anyone of our coworkers or supervisors. In my opinion I think it helps keep safety in the forefront of everyones mind and to shed light on safety issues others may not have thought of before.

I will start off the list myself and I will do my best to update the list in the first post of this topic for easey reading.

I would like to also share a 3 pillar ideology that my company rolled out this year as a base for our safety awareness program. They consist of these 3 subjects:

I. A culture of zero tolerance-- No injuries are exceptable. Everyone deserves the right to go home in the same condition they arrived in.

II. Safety is everyones resposibility-- Do not wait for someone else to bring a safety issue to someones attention. Do not wait to make a comment to someone that they may be doing something unsafe and suggest a safer method.

III. Every walk is a safety walk-- When your at your place of work or in a class keep your eyes open for possable safety issues and do something to fix it or make it known.

Feel free to bring these ideas to your place of work or into your classroom. :)
OK lets get this list started!

1. When working with electricity or testing equipment always where cotton (natural fiber) clothing including sox and underware to protect yourself from arc flash burns wich would melt synthetic clothes to your skin. If you are not whereing cotton clothing be sure to where a full length cotton lab coat.

2. Always where safety glasses.

3. Make sure to remove tools and garbage from your work area when energizeing a piece of equipment.

4. Use the correct tool for the job.

5. When energizeing a piece of equipment rope of the area to help alert others that work or testing is going on and to make it less likely someone will get an accidental shock.

6. Before testing call out loudely that you are "testing" to inform others in the erea that you are energizeing something.

7. When useing variable voltage test equipment make sure to check that it is switched off first and the voltage is turned down to the lowest setting. Make sure to do the same thing when you are finished.

8. Check your test equipment cords and leads for any cuts or cracks in the insulation or loose connections.

9. Ensure that your tools are in good working order.

10. Stay focused when you are working with live electricity it is easy to forget what you are doing and accidentaly touch something that you should not.

11. Do not where metal jewelry like rings and necklaces when working with electricity.

12. When working with electrical test equipment make sure you know the correct voltage that you should be useing and also weather it is AC or DC voltage to prevent damage to to the equipement being tested.

OK thats enough for me for now. Lets hear some ideas from our fellow CEans! :)

SAFETY IS EVERYONES RESPONSIBILTY.

Boiler Control Theory (Feed water Control)

Posted: 24 Dec 2010 10:39 AM PST

Boiler Control Theory (Feed water Control)

The feed water is controlled to keep the drum level .






Water-level controls continuously monitor the level of water in a steam boiler in order to control the flow of feed water into the boiler and to protect against a low water condition which may expose the heating surfaces with consequent damage. The control may be float operated but modern plant will have conductivity probes. The probes will be fitted in pads or standpipes on the crown of the shell or drum and enclosed in a protection tube which will extend to below the lowest water level.
With watertube boilers the control of the water level needs to be precise and sensitive to fluctuating loads due to the high evaporative rates and relatively small steam drums and small water content.




(1) One element control
One element control using only the drum level is applied during the low load (< 20-25&#37; boiler load).

before we talk about the control theory of one element control , we have to show the (SHRINK and SWELLING) phenomena which is happened at boiler drum ,whenever you start firing the boiler:-

To illustrate the shrink and swell effect in a steam drum let us consider a sharp increase of steam consumption. With the sudden increase in the steam consumption the steam drum pressure drops immediately. With the sudden drop in the pressure the steam bubbles in the water wall and the drum swell and results in a sharp momentary increase in the drum level. After the pressure stabilizes the drum levels behaves in a conventional manner. This initial increase in the level is called swell and it is unique to the steam drum.








Similarly, when the steam consumption reduces suddenly, the drum pressure rises immediately and the steam bubbles in the water shrink. This leads to a sharp momentary decrease in the drum level. This initial decrease in the steam drum level is called shrink.








In a conventional one-element control strategy the output of a level controller cascades into a flow controller. Consider now the use of a conventional one-element control strategy to control the steam drum level. As the drum level increases the controller reduces the feed water supply. And similarly, if the drum level decreases the controller increases the feed water supply. Let us assume that the steam consumption increases suddenly. Due to the swelling effect the steam drum level will rise initially and then decrease. The controller will initially reduce the feed water supply. This will in effect reduce the water inventory and after the swell effect the water drum level will drum significantly.










This is a disadvantage of one element control system , therefore we use only this system structure at (20 to 25 % load) , and we have to take care of drum level by controlling the start up blow off valves. So, to eliminate such this problem , another control scheme is applied to eliminate the drawbacks of one-element control at higher loads.



(2) Three element control
Three element control using the followings is applied during the normal operation (> 20-25% boiler load )
- Drum level
- Main steam flow
- Feed water flow


In order to handle the situation, the steam flow rate should also be considered for drum level control. It can be done by adding the steam flow rate as a feed forward signal to the output of the level controller. Hence, the supply of the feed water flow is compensated for changes in the steam flow rate demand. With this strategy as the steam flow rate changes the demand for the feed water flow rate also changes in the right direction and minimizes the effect of shrink and swell on the drum level.






Now, let us assume that the steam consumption increases suddenly. As the steam consumption increases the feed forward signal increases the feed water supply to the steam drum. Due to the swell effect the level controller reduces the feed water supply. The net effect of the three-element level control scheme changes the feed water supply appropriately and reduces the effect of swell on the drum level. Thus, the three-element level control strategy provides a more stable drum level control.

Learning to use a digital multimeter

Posted: 24 Dec 2010 08:04 AM PST

Can anyone recomend an online educational source (interactive if possable) to fully learn How, Why and Where to use a Digital Multimeter and all its functions. I have a small amount of experiance with them but mostley by hands on and for checking continuity.

Intelligent Vehicular Monitoring Using Multi-Hop Wireless System

Posted: 24 Dec 2010 05:31 AM PST

ABSTRACT:-

The accurate location of the accident spot is the key for the correct evaluation of a link between road and accident process and for right choice of improvement measures in vehicular monitoring systems.
A Multi-hop based wireless adhoc network of nodes can disseminate critical safety information in alert packets. The nodes can be embedded in vehicles. The alert can be used to trigger emergency responses resources. For example, the network can signal unusual events such as accidents, disabled vehicles or road obstructions to operators in nearby vehicles. When the vehicles are equipped with the wireless nodes, the information can easily be broadcast and propagated along the road until the desired destination service center is reached.
Now this concept is used in vehicular accidents to get a medical emergency assistance. When an accident occurs on a road, this is sensed as an event in both victimized vehicles (source node) and an alert packet is broadcast in response to sensing the event. This alert packet is received by a set of candidate nodes (nearby passing vehicles) within a broadcast range of a source node. Each candidate node infers distance between the candidate node and the source node based on the receive power of received alert packet and determines a priority for rebroadcasting the alert packet, wherein the priority is based on the distance to minimizing a probability of collisions while rebroadcast the alert packet and extend a range of the broadcasting.
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