The process steps are numbered for reference. Statistical Process Control is based on the analysis of data, so the first step is to decide what data to collect. There are two categories of control chart distinguished by the type of data used: Variable or Attribute.
Variable data comes from measurements on a continuous scale, such as: temperature, time, distance, weight. A critical but often overlooked step in the process is to qualify the measurement system. No measurement system is without measurement error. If that error exceeds an acceptable level, the data cannot be acted upon reliably. Using this erroneous data, the process was often adjusted in the wrong direction - adding to instability rather than reducing variability. See the Measurement Systems Analysis section of the Toolbox for additional help with this subject.
Develop a sampling plan to collect data subgroups in a random fashion at a determined frequency. Be sure to train the data collectors in proper measurement and charting techniques. If process variation e. The type of chart used will be dependent upon the type of data collected as well as the subgroup size, as shown by the table below. A bar, or line, above a letter denotes the average value for that subgroup. Likewise, a double bar denotes an average of averages. Consider the example of two subgroups, each with 5 observations.
Each process charted should have a defined reaction plan to guide the actions to those using the chart in the event of an out-of-control or out-of-specification condition. Read Section 10 below to understand how to detect out-of-control conditions. One simple way to express the reaction plan is to create a flow chart with a reference number, and reference the flow chart on the SPC chart.
Many reaction plans will be similar, or even identical for various processes. Following is an example of a reaction plan flow chart:. A control plan should be maintained that contains all pertinent information on each chart that is maintained, including:.
The control plan can be modified to fit local needs. A template can be accessed through the Control Plan section of the Toolbox. After establishing control limits, the next step is to assess whether or not the process is in control statistically stable over time.
In theory, they are tested before leaving the factory but I have seen many memory cards reported as being DOA. Consequently, I'd use a card for a couple weeks before shooting something vitally important like a wedding. Just thought I should include this short answer from Jeff Cable, as well. Jeff is a photographer and Lexar employee and wrote an answer to this question in a comment on the post from a few days ago.
Unless you format your card 10 times a day, it should last a lifetime. And…of course…if you have a Lexar Professional card, it has a lifetime warranty and can be replaced if anything does go wrong.
Thanks for this detailed response, especially the info on the write cycles. It makes sense that high frequency usage would compound wear and tear on the electronics.
Do you have any information on the lifespan of budget triggers like the Cactus V4? Maybe another blog post? I have a permanent solution for all of you. I have 12 4GB CF cards I have been using for three years, and will continue to use… but… I think I will buy some of those Lexar cards with the life time warranty for this years weddings!
This is my first response to one of your blogs but I wanted to say thanks for all of your information. I even have an old IBM micro-drive, both cards are used today in my D Please folks, something to keep in mind about any lifetime warranty: You might get the card replaced, but you might not get the data replaced.
The Grand Canyon? Sure, go ahead. Well, Never! Why would you need to format your card anyway? For those that are interested, wear levelling works a bit different than what most users think of it. In fact, wear is not spread out across all blocks evenly. Rather, when a block can no longer be written to, the controller inside the flash card detects this and allocates a spare block to replace that block, and internally remaps that block. This generally can not be detected by the hardware that is using the flash card the SD or CF controller and is totally transparent.
So in effect, a block is mapped out and replaced when one is needed. Not the most healthy of food choices linked to it either. Maybe suggesting purchasing shares of MasterCard rather than spending money on a credit card at Taco Bell would be a better post for you to teach young people about money. Now I agree, none of these perks matter if students pay interest, so they need to be able to responsibly use a credit card as a tool and pay their balance in full each month.
Please enable JavaScript in your browser. By: Tom Drake. Advertiser Disclosure. Tom Drake. Leave a reply Click here to cancel reply. In effect it wears out. There are a couple of different types of memory cell that can be used in solid state media.
High end professional media will often use single level memory cells that are either on or off. These cells can only store a single value, but they tend to be fast and extremely reliable due to their simplicity. But you need a lot of them in a big memory card. The other type of cell found in most lower cost media is a multi-level cell. Each multi-level cell stores a voltage and the level of the voltage in that cell represents many different values.
As a result each cell can store more than one single value. The memory cells are insulated to prevent the voltage charge leaking away.
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