Breaking News
Comments
Newest First | Oldest First | Threaded View
Page 1 / 3   >   >>
Robert.Groh
User Rank
Author
Re: Lot's more to consider when picking resistors
Robert.Groh   12/11/2013 10:31:47 AM
NO RATINGS
You are absolutely correct.  Frankly it is a topic that would take a lot more words than you could cram into a single column or blog.  One of the main points to be made is that (seemingly ... and I could be wrong) many design engineers are not aware of all the factors that affect the individual parts that we use.  It is also true that many of these effects are small relative to the 'big' hitters but, until you get a more comprehensive picture, you don't know what you can ignore! In my 50+ years of electronics design, I have been constantly surprised by undiscovered factoids.  Ah, life can be interesting!

And, yes, the wood working went well.

Adam-Taylor
User Rank
Author
Re: Lot's more to consider when picking resistors
Adam-Taylor   12/11/2013 3:01:41 AM
NO RATINGS
Robert thank you for the very detailed response. You are correct there are a number of other paramters that one must consider for a compete design.

However, the article was mainly looking at worse case analysis, which typically covers such things as tolerance and drift and the effects upon the peformance of the circuit.

There is another blog which Max will hopefully be pulling across from the old programmeable logic design line which addresses the reliability and part stress anaylsis.

Typically the reliability analysis would look at the component failure rate, however this could be either a parts count or stressed reliability in which case the voltage, current and power rating of the resistor would be considered from the part stress analysis.

I should do a blog showing how all these are interconnected and analysed to demonstrate a reliable system.

I hope the wood work was fun ;)

seaEE
User Rank
Author
resistance is futile and sometimes fusible
seaEE   12/11/2013 12:23:37 AM
NO RATINGS
With low value leaded resistors, the measurement point on the leads is sometimes specified since the temperature coefficient of the leads can contribute significantly to the measurement.  With the old venerable Allen Bradley carbon composition resistors, humidty could affect the resistance value as the carbon comp material would absorb the humidity and change the value.  Baking the resistors for several hours would drive out the moisture and reveal the resistor's true value.

 

Robert.Groh
User Rank
Author
Lot's more to consider when picking resistors
Robert.Groh   12/10/2013 10:25:24 PM
NO RATINGS
Your discussion is essentially correct but does not include everything that should be included if you are going to do a really complete job.  Just off the top of my head here is my list:

Resistor tolerance (which you covered nicely although the statiscal distribution may be of importance - I usually just assume a square distribution - i.e. it is equally likely that the resistor value will be anywhere within it's specified range).

Power Rating (including the derating factors for high temperature - some resistor types start to derate at 25 degC and are rated at zero dissipation at 100 degC). You need to do a check on the in circuit power dissipation of ALL your resistors.

Temperature range

Voltage rating (some resistor types are only good for 50 V or so - might not be a problem but you need to be aware of it).

Reliability (and the impact of all the stress factors on the reliability).

Current ratings - short impulse as well as long term (e.g. heating) (a 10A, 100 ns wide pulse may not exceed the power rating of a small resistor but it might very well blow it to bits).

Changes in value to stuff like the thermal shock of being soldered into your circuit.

Noise effects

Non-linearity (e.g. variations in resistance with applied voltage).

Effects of shock (on reliability, etc).

Probably more but it is late at night and I have some wood working to do.

 

MeasurementBlues
User Rank
Author
Re: Is that you?
MeasurementBlues   12/10/2013 9:21:18 AM
NO RATINGS
"I am thinking of bring back hats as well like the trillby or maybe a nice bowler hat as well"

I'll stick with a baseball cap.

Adam-Taylor
User Rank
Author
Re: Resistors aren't resistors
Adam-Taylor   12/10/2013 6:47:05 AM
NO RATINGS
It is worth noting that these parameters still need to be considered for the effects upon perofmance and stability within AC circuits.

Adam-Taylor
User Rank
Author
Re: Is that you?
Adam-Taylor   12/10/2013 3:25:52 AM
NO RATINGS
I am thinking of bring back hats as well like the trillby or maybe a nice bowler hat as well

Adam-Taylor
User Rank
Author
Re: Resistors aren't resistors
Adam-Taylor   12/10/2013 3:21:35 AM
NO RATINGS
@Measurement Blues,

You are correct this does assume we are working at DC, I was going to follow it up with one looking at AC but this would look at other discretes as well as once frequency is introduced you need to consider the parasitics

MeasurementBlues
User Rank
Author
Seebeck Effect
MeasurementBlues   12/9/2013 10:39:26 PM
NO RATINGS
Adam mentions Seebeck Effect, see

Thermocouples: Simple but misunderstood

MeasurementBlues
User Rank
Author
Re: Is that you?
MeasurementBlues   12/9/2013 10:36:54 PM
NO RATINGS
Adam wears a tie to work? How 1990s.

Page 1 / 3   >   >>


Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
Radio
LATEST ARCHIVED BROADCAST

What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.

Brought to you by:

Most Recent Comments
Like Us on Facebook
Special Video Section
In this short video we show an LED light demo to ...
02:46
Wireless Power enables applications where it is difficult ...
07:41
LEDs are being used in current luxury model automotive ...
With design sizes expected to increase by 5X through 2020, ...
01:48
Linear Technology’s LT8330 and LT8331, two Low Quiescent ...
The quality and reliability of Mill-Max's two-piece ...
LED lighting is an important feature in today’s and future ...
05:27
The LT8602 has two high voltage buck regulators with an ...
05:18
Silego Technology’s highly versatile Mixed-signal GreenPAK ...
The quality and reliability of Mill-Max's two-piece ...
01:34
Why the multicopter? It has every thing in it. 58 of ...
Security is important in all parts of the IoT chain, ...
Infineon explains their philosophy and why the multicopter ...
The LTC4282 Hot SwapTM controller allows a board to be ...
This video highlights the Zynq® UltraScale+™ MPSoC, and sho...
Homeowners may soon be able to store the energy generated ...
The LTC®6363 is a low power, low noise, fully differential ...
See the Virtex® UltraScale+™ FPGA with 32.75G backplane ...
Vincent Ching, applications engineer at Avago Technologies, ...
The LT®6375 is a unity-gain difference amplifier which ...