Posts Tagged ‘engineering calculations’

Transistors – Voltage Regulation Part VI

Sunday, August 26th, 2012
     Believe it or not as a kid in grade school I used to hate math, particularly algebra.  None of my teachers were able to decipher its complexities and render it comprehensible to me or the majority of my classmates.  Then in high school everything changed.  I had Mr. Coleman for freshman algebra, and he had a way of making it both understandable and fun, in a challenging kind of way.  With 40 years of teaching under his belt, Mr. Coleman knew exactly how to convey the required information in an understandable manner, and to this day I find his insights useful in solving engineering calculations.

      Last time we began our discussion on Ohm’s Law and how it may be applied to our example circuit to solve for the electrical current flowing through it.  Let’s continue our discussion to see how the Law applies to only one part of the circuit.  Then, we’ll use a little algebra to show how the output voltage of an unregulated power supply is affected by changes in RTotal.

electronic power supply

Figure 1


     To help us see things more clearly, in Figure 1 we’ll cover up the inside workings of the unregulated power supply side of the circuit and concentrate on the external supply part of the circuit alone.  Since RTotal is connected to the terminals of the power supply, the voltage applied to RTotal is the same as the power supply output voltage, VOutput.

     In my previous article, we learned that according to Ohm’s Law, the current flowing through a resistance is equal to the voltage applied to it, divided by the resistance.  The fact that RTotal is connected to the two output terminals like we see in Figure 1, allows us to use Ohm’s law to solve for the electrical current, I, flowing through  RTotal:

I = VOutput ÷ RTotal

     Now let’s pull the cover off of the unregulated power supply again to see what’s going on within the circuit as a whole.

electronic circuit

Figure 2


    In Figure 2 we can see that the current, I, flowing through RTotal is the same current flowing through the balance of the circuit.  In the preceding blog we found that value to be:

I = VDC ÷ (RInternal + RTotal)

     We can combine the above two equations for I to develop an algebraic relationship between VOutput and RInternal, RTotal, and VDC:

VOutput ÷ RTotal   =  VDC ÷ (RInternal + RTotal)

     Then, by rearranging terms and applying the cross multiplication principle of algebra we can solve for VOutput.  This involves multiplying both sides of the equation by RTotal:

VOutput =  RTotal × (VDC ÷ (RInternal +RTotal))

     This equation tells us that although RInternal doesn’t fluctuate, VOutput will fluctuate when RTotal does.  This fact is demonstrated in our equation when we make use of algebra.  That is to say, when a term changes on one side of the equation, it causes the other side of the equation to change as well.  In this case, when RTotal  changes, it causes VOutput to change in proportion to the fixed values of VDC and RInternal.

     Next time we’ll look at another shortcoming of unregulated power supplies, more specifically, how one supply can’t power multiple electrical circuits comprised of different voltages. 


Food Manufacturing Challenges – HACCP Design Principle No. 7

Sunday, November 27th, 2011
     Ever overdraw on your checking account or max out a credit card?  It’s not hard to do if you’re not keeping track of things.  How can we manage household expenses without some sort of record keeping?

      Away from home, in the business sector, record keeping becomes even more important.  In fact, it’s the very thing covered by HACCP Design Principle No. 7. 

     Principle 7:  Establish record keeping procedures. – This HACCP principle requires that all food manufacturing plants maintain records to show they implemented a HACCP plan, are following all principles, and the plan is working effectively.

     Let’s look at an example.  In keeping with the directive of HACCP Design Principle 7, the engineering department of a food manufacturing plant must keep records for each design project.  The design record for a new cookie forming machine would contain things like engineering calculations to determine strength requirements of machine parts and supports, as well as power requirements for the electric motor that drives the machine.  This design record would also contain documentation concerning materials selected to construct the machine, as well as dimensioned mechanical drawings of the machine and its parts.  These dimensioned drawings will show all physical dimensions of the machine and its constituent parts. 

     The record would also contain test results and analysis of the results.  Lastly, the design record must include a risk analysis of potential hazards that could result.  Other activities include identification of CCPs, establishment of critical limits, and other factors in accordance with HACCP Design Principles 1 through 5.  In other words, the record must be complete, bearing witness to an effective adherence to HACCP Design Principles 1 through 5. 

     Principle 7 also encompasses guidelines set in place through Design Principle 6, which calls for the establishment of procedures to govern Principles 1 through 5.  A complete record would contain the procedures themselves, along with any revisions.  It would also contain documentation that the procedures were reviewed and approved by management along the way.

     Finally, of what use would records be if they were incomplete, disorganized, and outdated?  A document control system not only establishes procedures, but assigns responsibilities to personnel within the department for filing design records to make sure that everything is up to snuff.  This system would encompass everything, from the creation of engineering documents, to their timely entry into the record keeping system.

     We have now exhausted our discussion on HACCP Design Principles.  We’ll switch to a new topic next time, examining some basic concepts behind the control of industrial equipment and machinery.