1. Residential Metering: iPERL vs Ultrasonic meters

2. Technology choice Magnetic technology Ultrasonic technology
Small sizes allow
Higher field from battery
Higher turndown
Better repeatability
Compact sensor
Short lay lengths
Ultrasonic technology
Large sizes allow
No mirrors in flow path
Timing resolution easier
Multiple beam paths
Flow profile immunity

3. How ultrasonic meters work
Time of flight with and against flow
Sound travels up to 0.5% faster with flow at Q4
Time difference is <1ns at lowest flow rate Q1
Small meters all use mirrors in the flow path
Complex flow profiles around the mirrors
Direct sound path
Mirror

4. Ultrasonic meter: flow profile
Velocity profile of water varies substantially across the flow path.
This profile changes with flow rate, temperature and pipe conditions
Ultrasonic meters try to “average” the velocity, but this is not perfect.
Typical non linearity pre-correction is 20-30%
Correction needs multiple calibration parameters

5. Small ultrasonic meters – low flow
Path lengths are relatively short
Small time differences at lowest flow (e.g. 300ps)
3% accuracy: 10ps time stability (0.003° at 1MHz) Extremely hard to achieve
Multiple effects contribute – e.g. transducer mounting
Zero point calibration required
Set during manufacture
Unclear how stable this is
As the water temperature varies
As the electronics temperature varies
Over 20 years

6. Badger E-series vs iPERL
Direct comparison
Tested in series on the same flow bench
Both repeatability and error curve different
Badger E-series
iPERL

7. Real world installations
Not like a lab test bench
Valves next to the meter
Elbows, adapters
Unusual orientations
Air bubbles
Varying water temperature
Vibration
Highly intermittent flow
Sometimes in reverse
Dirt, debris and scale
Bow Mar Water

8. Orientation effects
Kamstrup Multical

9. Swirl and partial obstruction
No effect on iPERL
Upstream left and right swirl & orifice
Affects ultrasonic meter at high flow rates
Kamstrup Multical
iPERL

10. Entrained air No effect on iPERL Bubbles scatter sound beams
450 ml/hour
Bubbles scatter sound beams
Kamstrup Multical
iPERL

11. Water temperature No effect on iPERL Known effects in ultrasonic
Internal corrections to compensate not perfect
Kamstrup Multical
iPERL

12. Vibration No effect on iPERL
22, 50 Hz
Influences ultrasonic meters at low flow rates
Hydrometer Hydrus
iPERL

13. Real-world intermittent flow
Ultrasonic meters sample every ~second
Measures instantaneous flow without averaging
iPERL samples continuously
Captures short duration flows
Averages the flow correctly
Ultrasonic
iPERL

14. iPERL compared to small ultrasonic
Parameter
iPERL
Small Ultrasonic Meter
Linearity with flow
Linear by design
Complex internal linearization
Installation
No restrictions on orientation by design
Some restrictions to avoid trapped bubbles
Effect of flow disturbances
No effect – always averages the flow by design
Susceptible to errors from flow profile
Temperature
Minimal effect by design
Complex internal corrections needed for viscosity and speed of sound
Vibration
Does not affect accuracy
Can impact accuracy
Intermittent flow accuracy
Continuous sampling and averaging
Discontinuous snapshots can cause errors
Particulates
Robust, >400x better than PD
Many parts inline that could be damaged
Low flow accuracy
Accurate by design at low flow
Dependent on stability of offset calibration
Empty Pipe
Reliably detected
Triggered by air space next to transducers
Long term accuracy
Maintained by design
Highly dependent on good design