Demo (Instrumentation Damping)
This training tool is provided for educators, instructors, students, and practitioners who want to better understand the concepts of damping and associated responses. The simulation is somewhat simple (due to coding limitations of author), but it does a good job of showing the impact of damping settings for both step response situations (such as during a calibration check) and for dynamic situations. The noise is configurable via the NOISE tab and the damping and raw input value can be manipulated on the MAIN CONTROLS tab. There is some helpful information on the other tabs as well.
The initial values are with minimal damping and some typical noise - try filtering it out with damping; see the effects as you vary the raw input; adjust the noise parameters in the Noise tab. Read more in the other tabs. Our goal is always to help folks learn and grow - hope this is useful. Check it out and let us know your thoughts.
Instructors: By using the Pause Buttons and the included X-Y measurement grid, you can demonstrate things like the 63% concept in time constants, and more. Tons of options. We will be publishing other great demo tools in the near future (PID controls & Tuning Demo, Valve Positioner Problems Demo, Smart Transmitter Calibration Concepts Demo, Zero/Span Errors Demo, and many more). Follow us on LinkedIn to see each new blog, demo, and more.
Play. Have Fun! Learn by Doing!
Process Transmitter Damping Simulator
About Noise Parameters:
Noise Amplitude (%) - How big the noise swings are compared to your span:
- Small (0.1-0.5%): Mimics high-quality transmitters in clean environments
- Medium (1-2%): Typical of most field instruments with normal interference
- Large (3-5%): Represents challenging installations with electrical interference or turbulent processes
- Very large (5-10%): Problematic installations that definitely need filtration
Center Frequency (Hz) - How fast the noise changes:
- Very low (0.01-0.1 Hz): Very slow changes (minutes) - like gradual process drift
- Low (0.1-1 Hz): Slow oscillations (seconds) - like process cycling or mild turbulence
- Medium (1-5 Hz): Moderate speed changes - typical process noise
- High (5-20 Hz): Fast changes - electrical noise, vibration
- Very high (20-60 Hz): Very fast changes - AC power interference, pump/motor harmonics
Distribution Width - How varied the noise frequency is:
- Narrow (1): Noise is concentrated at a specific frequency (like a 60Hz hum)
- Medium (2-3): Noise spread across a range of frequencies (typical of most real processes)
- Wide (4-5): Noise spread very broadly (like white noise or random process variations)
In real-world applications, you'll often encounter multiple types of noise simultaneously. The best damping setting is one that filters out the noise without making your instrument respond too slowly to actual process changes.
Understanding Time Constants in Simple Terms
A time constant is like a "responsiveness setting" for your instrument. It determines how quickly your transmitter responds to changes in the process.
Practical Example: Temperature Probe
Imagine dipping a temperature probe from cold water (40°F) into hot water (140°F):
- 0.5 second time constant: Reaches ~100°F in 1 second, ~130°F in 2 seconds
- 2 second time constant: Reaches ~70°F in 1 second, ~100°F in 2 seconds
- 5 second time constant: Reaches ~60°F in 1 second, ~75°F in 2 seconds
A longer time constant means slower response but better noise filtering.
Practical Example: Pressure Transmitter
A pressure transmitter monitoring a pump system:
- 0.2 second time constant: Shows each individual pump pulse but might be "noisy"
- 1 second time constant: Smooths out pump pulses while still responding to valve changes
- 3 second time constant: Very stable reading, but might miss brief pressure events
Time Constants and Instrument Calibration
When calibrating an instrument, you should always wait at least 7 to 10 time constants between check points to ensure that the process has truly stabilized. Here's why:
| Number of Time Constants | % of Final Value Reached | % Error Remaining |
|---|---|---|
| 1 | 63.2% | 36.8% |
| 2 | 86.5% | 13.5% |
| 3 | 95.0% | 5.0% |
| 4 | 98.2% | 1.8% |
| 5 | 99.3% | 0.7% |
| 6 | 99.8% | 0.2% |
| 7 | 99.9% | 0.1% |
| 8 | 99.97% | 0.03% |
| 9 | 99.99% | 0.01% |
| 10 | 99.995% | 0.005% |
For high accuracy measurements, wait at least 7 time constants after any change before taking a reading.
Think of a time constant like a capacitor charging - it follows a curve rather than an immediate change. After one time constant, the reading moves about 63% of the way to the new value.
FOR NERDS ONLY: THE MATH BEHIND TIME CONSTANTS
The basic first-order filter equation is:
y(t) = y(t-1) + (1/τ) * (x(t) - y(t-1)) * Δt
Where:
y(t)is the filtered valuex(t)is the raw input valueτis the time constant (in seconds)Δtis the time step between calculations
This is a digital approximation of the differential equation: τ * dy/dt + y = x
For a step change, the solution is: y(t) = y₀ + (y∞ - y₀)(1 - e^(-t/τ))
Notes & Explanations
About This Simulator
This simulator was created by Mike Glass with Orion Technical Solutions as a tool to help instructors, trainers, students, and practitioners better explain and demonstrate the impacts of noise and proper damping since it is such a common problem across nearly all industries.
This simulator demonstrates how process transmitters use damping (time constants) to filter out noise while still tracking actual process changes.
You can:
- Adjust the raw process value to see how quickly the filtered value responds
- Change the time constant to see different damping behaviors
- Configure realistic instrument noise parameters
- See the differences between raw and filtered signals
Choosing the Right Time Constant
Too Small: The transmitter responds quickly but passes too much noise
Too Large: The transmitter filters noise well but responds too slowly to actual changes
Just Right: Balances noise reduction with appropriate responsiveness for your process
Typical Values in Industry:
- Fast processes (flow, pressure): 0.2-1.0 seconds
- Medium processes (temperature in small volumes): 1-3 seconds
- Slow processes (level, temperature in large vessels): 3-10+ seconds
Understanding Noise in Measurement
Real transmitters experience several types of noise:
- Process Noise: Actual variations in what you're measuring (turbulence, mixing issues)
- Sensor Noise: Electrical and thermal noise in the sensing element
- Electrical Noise: EMI, RFI, ground loops affecting signal transmission
- Quantization Noise: From analog-to-digital conversion
This simulator focuses primarily on transmitter-level noise and how damping affects the output signal.
About the author
Mike Glass
Mike Glass is an ISA Certified Automation Professional (CAP) and a Master Certified Control System Technician (CCST III). Mike has 38 years of experience in the I&C industry performing a mix of startups, field service and troubleshooting, controls integration and programming, tuning & optimization services, and general I&C consulting, as well as providing technical training and a variety of skills-related solutions to customers across North America.
Mike can be reached directly via [email protected] or by phone at (208) 715-1590.