Please could someone define slew rate?

WBahn

Joined Mar 31, 2012
24,854
sorry I put flew in title, meant flew rate
This doesn't really clear things up.

Do you mean:

a) Slew rate
b) Flew rate
c) Flow rate
d) something else

If you mean slew rate, it is simply the fastest rate at which a signal, usually the output of an amplifier or some other circuit, can change. If an amp has a slew rate of 10 V/μs and has a gain of, say, 1000, then the fastest that the input signal can change is 10 V/ms. Anything faster and the output will not be able to change fast enough to produce an output signal that is a faithful replica of the input signal waveform -- i.e., distortion will result. This then puts limits on the amplitude and frequency combinations that the amplifier can process without introducing slew-rate distortion.
 

MrChips

Joined Oct 2, 2009
19,417
Slew, like baud, is already a rate. Hence adding "rate" is redundant.

Slew is Δv / Δt.
Units are volts per second, or usually volts per micro-second.
 

WBahn

Joined Mar 31, 2012
24,854
Slew, like baud, is already a rate. Hence adding "rate" is redundant.
Do you happen to have an authoritative (ore reasonably close) source for that?

The basic definition of 'slew' that applies is simply a change by a large amount. Another that might apply is a violent or awkward turning or sliding. I've never seen any text or datasheet (that I recall) use any term other than "slew rate". If I Google for "electronics dictionary slew rate" I get LOTS of hits that are electronics-specific. If I put a minus in front of the word rate I get none (on the first couple pages) that are electronics-specific at all and most of the ones I looked at at the work "electronic" in there coincidentally. Other common uses of the word, such as slew bearing, also use it to refer to a type of change with little or nothing to do with the rate of change.

Note that this is completely consistent with saying that the output of an amplifier is slewing at 20 V/μs.
 

MrChips

Joined Oct 2, 2009
19,417
The amplifier's output is slewing at 20V/μs. We don't say the amplifier is slew rating at 20V/μs.

We say a car's speed is 60mph. The car is speeding at 60mph.
We don't say the speed rate is 60mph.

Slew rate and baud rate are examples of poor grammar, regardless of common usage.
 

MrChips

Joined Oct 2, 2009
19,417
On second thoughts, it is not poor grammar. It is bad math.

Speed rate such as 10mph/s means acceleration.

Thus, slew rate such as 20V/μs/s would also mean accelerating voltage, not linearly increasing voltage.
 

WBahn

Joined Mar 31, 2012
24,854
The amplifier's output is slewing at 20V/μs. We don't say the amplifier is slew rating at 20V/μs.
Nor would we. Just as we wouldn't say that an aircraft that had a roll rate of 60°/sec was roll rating at 60°/sec, we would say that it was rolling at 60°/sec.

You've done nothing but reinforced my case.

We say a car's speed is 60mph. The car is speeding at 60mph.
We don't say the speed rate is 60mph.
If someone says that the car is speeding at 60 mph they almost certainly do not mean that the speed of the car is 60 mph, but rather that at a speed of 60 mph the car is speeding (i.e., exceeding the speed limit) or some other implied use where the word "speeding" is not directly tied to the 60 mph, such as the car is speeding (down the road) at 60 mph.

And, no, we don't say that the speed rate is 60 mph because speed IS a rate.

Slew rate and baud rate are examples of poor grammar, regardless of common usage.
Then it should be a trivial matter to come up with all kinds of references from at least some of the hundreds of sites dedicated to proper grammar and used to back up the claim that "slew rate" is improper.
 

WBahn

Joined Mar 31, 2012
24,854
On second thoughts, it is not poor grammar. It is bad math.

Speed rate such as 10mph/s means acceleration.

Thus, slew rate such as 20V/μs/s would also mean accelerating voltage, not linearly increasing voltage.
Only if you use YOUR preferred definition of "slew" as meaning the quantitative rate at which a single changes. Please cite some reasonably authoritative sources that support YOUR preferred definition. If you are right, then that should be very easy to do.
 

nsaspook

Joined Aug 27, 2009
6,503
Maybe it would be instructive to think about the origins of the term. In naval parlance 'slew' just means turning on a fixed point. A 'slew' rate would be how fast. IMO the usage predates electronics.
 

MrChips

Joined Oct 2, 2009
19,417
Maybe it would be instructive to think about the origins of the term. In naval parlance 'slew' just means turning on a fixed point. A 'slew' rate would be how fast. IMO the usage predates electronics.
Ok, I can live with that.

Next question, why do people say "baud rate" instead of "baud"?
 

jpanhalt

Joined Jan 18, 2008
8,114
Ok, I can live with that.

Next question, why do people say "baud rate" instead of "baud"?
Same reason they insist on adding a "unit" to an atomic weight (which properly should be called a ratio): Habit.

I did look up the word, slew. It dates back quite awhile and has several meanings. "Rate" is not inherent in the term, regardless of its use. There has been a slew of responses on this subject.
 

LvW

Joined Jun 13, 2013
878
Hi I am struggling to understand what slew rate is, please could somebody write a basic definition?
In most cases, the slew rate is an inportant parameter to describe the performance of opamps - under the following conditions:
1.) The opamp is eqipped with a resistive feedback network - in most cases unity feedback.
2.) The input step must be large enough to drive the first stage of the opamp - immediately after applying the input step and before the feedback is active - into saturation. As a consequence, the first stage acts as a current source - as long as the delayed feedback signal is active and brings this stage back into the linear region.

Under these conditions, the output will exhibit a quasi-linear rise until the maximum is reached. The slope of this output signal is defined as SLEW RATE (given in V/µs).
 
Last edited:

atferrari

Joined Jan 6, 2004
3,489
Do you happen to have an authoritative (ore reasonably close) source for that?

The basic definition of 'slew' that applies is simply a change by a large amount. Another that might apply is a violent or awkward turning or sliding. I've never seen any text or datasheet (that I recall) use any term other than "slew rate". If I Google for "electronics dictionary slew rate" I get LOTS of hits that are electronics-specific. If I put a minus in front of the word rate I get none (on the first couple pages) that are electronics-specific at all and most of the ones I looked at at the work "electronic" in there coincidentally. Other common uses of the word, such as slew bearing, also use it to refer to a type of change with little or nothing to do with the rate of change.

Note that this is completely consistent with saying that the output of an amplifier is slewing at 20 V/μs.
Maybe it would be instructive to think about the origins of the term. In naval parlance 'slew' just means turning on a fixed point. A 'slew' rate would be how fast. IMO the usage predates electronics.
I've have worked in the distant past with freighters (Freedom type) fitted with "slewing cranes", pretty similar to these used in construction:

crane.jpg

I've seen them, who knows why, mentioned as "universal cranes". Not very practical but quite safe with bad drivers.
 

nsaspook

Joined Aug 27, 2009
6,503
Ok, I can live with that.

Next question, why do people say "baud rate" instead of "baud"?
For "baud" I would agree with you that rate is unnecessary in most cases where a speed is expressed. We were trained to just use 'baud' in reference to circuit speeds (X baud instead of baud rate at X). If message traffic was falling behind in transmission deliveries then we might say, "we need to increase the baud rate" of a circuit as a reference to the circuit type instead of a specific rate.
 
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