Friday, September 4, 2009

Safety Systems and Fail safe

Understanding the Fail-Safe Concept
Principle of SafetyThe fail-safe concept monitors the sensor status at all times. In the event of a failure, the fail-safe concept will simulate a protected position. The “protected” position is when the sensor is activated (closed) and the “normal” or “run” position is when the sensor is not activated (open).

- Normal Conditions – constant current flow (I) holding relay coil (K1) energized- Loss of Power – no current flow (I) and relay coil (K1) is de-energized- Actuation of Sensor – relay coil (K1) is shorted and de-energized- Failure of Sensor in the closed position – relay coil (K1) is shorted and de-energized- Failure of Sensor in the open position – (broken wire, switch or conductor) interupts current flow (I)and relay coil (K1) is de-energized- Resistor R – limits current flow through the sensor when actuated
Fail-Safe (4 wire system)
Fail-Safe is a shorthand term used to mean Fail to a Safe condition. In machinery with known hazards, the system is fail-safe when any failure leaves the machinery in a safe condition. The 4-wire fail-safe concept is illustrated in the figure above. A small current is constantly flowing through the sensor at all times, holding the relay coil energized at all times. The machine controls, interrupt, or stop circuitry is connected to the contacts of this relay. If the sensor is actuated, the relay coil will be shorted, causing the relay to deenergize. A resistor in series provides current limiting from overdrawing the power supply and limits the current through the sensor in the actuated position. If the sensor fails in the closed position the relay will be shorted and cannot be energized until the failure is corrected. If the sensor fails in the open position, the current path for the relay coil no longer exists and the relay coil cannot be energized until the current path is restored and the failure corrected.
In addition to the safety aspects achieved with Fail-Safe, it also provides:
- Isolation of the machine controls and sensor(s)- Isolation of high amperage and high voltage machine switching from the low voltage sensors- Conversion of a normally-open switch to required normally closed machine controls
Tapeswitch manufacturers safety light curtains, safety mats and safety Tapeswitches.

Thursday, September 3, 2009

UPS - Uninterruptible Power Supply

Green… Green… Green, today that seems to be a constant mantra that we are hearing from various sectors such as Government, Construction, and Consumers. Being Green is not an exotic disease that leaves your complexion looking like a Martian. Rather being Green is about conserving our valuable resources. Our resources are being depleted at a rate that some say will cause us to run out of resources very soon. I don’t know that I would be like Chicken Little running around screaming that the sky is falling, but we do need to take heed to the problems that do exist, and do what we can to conserve the resources we still have.

This brings me to my subject, Efficiency in UPS Systems. As I look through the trade magazines I have noticed that more and more is being talked about having Data Centers and other areas of Critical Power Back Up systems to become more efficient. UPS systems are found in most business’ today whether they be large or small. They are needed to protect the critical power required for Computers, Emergency Lighting Systems, Laboratory Equipment and more. All are using electrical energy to provide an uninterruptible source of power to these critical systems.

In case you haven’t heard, our electrical power generation facilities are being stretched to capacity. Then on top of that we have a Congress that would like to institute a program called Cap and Trade into law. The effect of this will be less energy production and higher prices for what energy we can get. All these possible new regulations and current production capabilities mandates that we need to become more Energy Efficient, this is a must for all of us. Most UPS manufacturers are promoting that their units are energy efficient, but when we begin to compare them side by side you will notice that some do not meet the mark. In the past some have purchased their UPS systems based on Name Brand Recognition alone, this may not be the best approach if you are really interested in getting the best efficiency and performance from a UPS system. Just because a company is large and well known does not mean they have the best equipment. Also saving a buck in the purchase price may end up taking a big bit out of your wallet when paying for wasted electricity for years down the road. Remember the efficiency of the system is what will ultimately save you on your energy bill for back up power, and again in the cost of cooling and cooling capacity, because efficiency means less heat being generated. Also check the output power factor of a UPS unit. This will be the key factor in knowing how much real power (kW) you will have available for your equipment, because you don’t want to be doing this again in a year or so when up grading your servers or add other equipment. The Input Power Factor is extremely important if you are being billed from your utility a power factor penalty charge. Check out the Harmonic feed back level because this can cause problems with other equipment up stream from the UPS. All of these factors will also play a part in Generator selection.

When selecting a UPS you must first know what power requirements you need for today and tomorrow. What amount of floor space will you be willing to allocate for this equipment. How much Back UP Time will be required because this will dictate the battery requirements and additional space for their placement. Think about peripheral equipment such as Maintenance Bypass Switches, Transformers, Surge Suppression Devices, Power Distribution Units, UPS Management Software, Tie-Cabinets (Parallel Systems), and Air Conditioning.

UPS units come in many different sizes and typology. The most popular systems are True On Line Systems or Duel Conversion systems. These will provide you with the best protection and power conditioning for your equipment.

We have many different brands for you to choose from depending on your application requirements. If you want the best system for your application give us a call and we can help you identify your systems requirements and select the best UPS for the job. We deal in UPS systems daily as well as power related problems, and we are familiar with the changes that are occurring in the industry. Call Syd Orr at Anderson Bolds today for more information.