Microseconds (μs) – Standard
Milliseconds (ms)
Nanoseconds (ns)
Seconds (s)
Select the unit used on your oscilloscope's X-axis
Calculated Slew Rate
0.00 V/μs
Voltage Change (ΔV)
0 V
Time Change (Δt)
0 μs
function calculateSlewRate() {
// Get input values
var v1 = document.getElementById('voltage1').value;
var t1 = document.getElementById('time1').value;
var v2 = document.getElementById('voltage2').value;
var t2 = document.getElementById('time2').value;
var timeUnitMultiplier = parseFloat(document.getElementById('timeUnit').value);
var resultBox = document.getElementById('resultBox');
var errorMsg = document.getElementById('errorMsg');
// Reset display
resultBox.style.display = 'none';
errorMsg.style.display = 'none';
errorMsg.innerText = ";
// Validation
if (v1 === " || t1 === " || v2 === " || t2 === ") {
errorMsg.innerText = 'Please enter values for both points (Voltage and Time).';
errorMsg.style.display = 'block';
return;
}
var valV1 = parseFloat(v1);
var valT1 = parseFloat(t1);
var valV2 = parseFloat(v2);
var valT2 = parseFloat(t2);
if (isNaN(valV1) || isNaN(valT1) || isNaN(valV2) || isNaN(valT2)) {
errorMsg.innerText = 'Please enter valid numbers.';
errorMsg.style.display = 'block';
return;
}
// Calculate Deltas
var deltaV = Math.abs(valV2 – valV1); // Slew rate is typically magnitude
var rawDeltaT = Math.abs(valT2 – valT1);
if (rawDeltaT === 0) {
errorMsg.innerText = 'Time difference cannot be zero (infinite slope).';
errorMsg.style.display = 'block';
return;
}
// Convert time to Microseconds (μs) for the standard calculation
// Input multiplier converts input to Microseconds
// If input is μs (1), deltaT_us = rawDeltaT * 1
// If input is ms (1000), deltaT_us = rawDeltaT * 1000
// If input is ns (0.001), deltaT_us = rawDeltaT * 0.001
// If input is s (1000000), deltaT_us = rawDeltaT * 1000000
var deltaT_us = rawDeltaT * timeUnitMultiplier;
// Calculate Slew Rate (Volts per Microsecond)
var slewRate = deltaV / deltaT_us;
// Display results
document.getElementById('slewRateResult').innerText = slewRate.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 4}) + " V/μs";
document.getElementById('deltaVResult').innerText = deltaV.toLocaleString('en-US') + " V";
document.getElementById('deltaTResult').innerText = deltaT_us.toLocaleString('en-US', {minimumFractionDigits: 3, maximumFractionDigits: 6}) + " μs";
resultBox.style.display = 'block';
}
How to Calculate Slew Rate from an Oscilloscope Graph
Slew Rate (SR) is a critical parameter in operational amplifiers (Op-Amps) and other electronic circuits. It defines the maximum rate at which the output voltage can change in response to a step input signal. Understanding how to calculate this directly from an oscilloscope graph is essential for verifying component specifications and analyzing signal distortion.
Understanding the Slew Rate Formula
Mathematically, Slew Rate is the derivative of voltage with respect to time. When measuring from a linear section of a graph (such as the rising or falling edge of a square wave response), it can be approximated using the slope formula:
SR = ΔV / Δt = (V₂ – V₁) / (t₂ – t₁)
Where:
ΔV (Delta V): The change in voltage (vertical axis).
Δt (Delta t): The change in time (horizontal axis) required for that voltage change.
Standard Unit: Volts per microsecond (V/μs).
Step-by-Step Guide: Reading the Graph
To obtain an accurate Slew Rate measurement from your oscilloscope trace, follow these steps:
Isolate the Transition: Adjust your oscilloscope time base (horizontal scale) to zoom in on the rising or falling edge of the waveform. The edge should take up a significant portion of the screen.
Identify the Linear Region: Slew rate is the maximum rate of change. Locate the steepest, straightest part of the slope. Avoid the curved "knees" at the very start or end of the transition.
Select Two Points: Pick two points on this linear slope.
Point 1: Mark the voltage ($V_1$) and time ($t_1$).
Point 2: Mark the voltage ($V_2$) and time ($t_2$).
Calculate Differences: Subtract the values to find the vertical height ($\Delta V$) and horizontal width ($\Delta t$) between your two points.
Divide: Divide $\Delta V$ by $\Delta t$. Ensure your time units are converted correctly to microseconds to match standard datasheet specifications.
Example Calculation
Imagine you are testing an Op-Amp with a square wave input. You freeze the oscilloscope display on the rising edge.
You place a cursor at -2V (Point 1). The time cursor reads 10.5 μs.
You place the second cursor at +2V (Point 2). The time cursor reads 11.3 μs.
If an Op-Amp is driven by a signal that requires a rate of change faster than its Slew Rate limit, the output will not be able to keep up. This results in slew-induced distortion. The output waveform will appear triangular rather than square or sinusoidal, limiting the bandwidth and fidelity of high-frequency or high-amplitude signals.