Flow, metering and water loss

Can you add a data logger to an existing water meter?

• Check for a pulse output first. Many meters already have one fitted and unused.
• Pulse weight sets your resolution. One pulse per 10 litres cannot show a 2 litre per hour drip.
• No supply interruption. Fitting a logger does not require cutting into the pipe.
• Clamp-on is the alternative. Where there is no meter at all, or none in the right place.

How the pulse output works

A mechanical or electromagnetic meter measures volume internally. A pulse output simply exposes that measurement as a switch closure every time a fixed volume has passed, in the same way a tipping bucket rain gauge reports a fixed depth of rain.

The logger counts those closures and timestamps them. Multiply the count by the pulse weight, the volume each pulse represents, and you have consumption for any interval you choose. Because each pulse is timestamped rather than just tallied, the same data yields flow rate as well as volume.

Fitting one is a low disruption job. The connection is to a terminal or a sensor head, not into the pipe, so there is no cutting, no shutdown and no supply interruption. On sites where taking water off is genuinely difficult, that is often the deciding factor.

Why pulse weight is the specification to check

This is the detail that most often disappoints after installation, and it is worth resolving before ordering anything.

Pulse weight is the volume represented by one pulse, commonly one pulse per litre, per 10 litres, per 100 litres or per cubic metre. It sets the finest change the system can possibly see, and no amount of clever analysis recovers detail below it.

The consequence is concrete. On a meter emitting one pulse per cubic metre, a slow leak of a couple of litres an hour produces one pulse every three weeks or so. There is no interval analysis that turns that into a leak alert. On a meter emitting one pulse per litre, the same leak is a steady overnight trickle that is obvious within a night.

So the question to ask is not whether a meter has a pulse output, it is what the pulse weight is relative to the smallest thing you want to detect. Where the existing weight is too coarse, a retrofit head with a finer weight, or a separate clamp-on meter, is the route to the resolution you need.

When to clamp on instead

A pulse logger can only report what the existing meter measures, which means it inherits both the meter’s position and its condition.

If the meter sits at the boundary but the question is which building or which process is using the water, the pulse output cannot answer it, because sub-metering requires measurement at the sub-branches. If the meter is old and under-registering, the logger will faithfully record the under-reading. And where there is no meter at all on a line worth watching, there is nothing to connect to.

Clamp-on ultrasonic metering addresses all three. It attaches to the outside of the existing pipe and measures through the wall, so it can be placed wherever the measurement is actually needed rather than wherever a meter happens to exist, and it requires no cutting or shutdown. For retrofit sub-metering on live pipework it is usually the practical answer.