Lost in Translation: Where People Get DALI Wrong (4)

In episode one of the series I discussed the polarity of the DALI bus. Episode two was about application controllers. And episode three about what DALI-2 really is.

This fourth episode of DALI misconceptions is about energy data.

DALI drivers can report energy data. This is covered by the Part 252 specification. Most people refer to this as measured energy. DALI is digital, so must be precise. A driver reports the energy consumption so it must measure it, right?

Wrong!

Firstly, DALI Part 252 only defines the protocol and the data points. it does not say anything about accuracy of the data. This depends on the manufacturer, and some of them specify how accurate the reported values can be and some don't say anything. DALI Part 252 is definitely not a utility-grade data. It can be good for general estimates and definitely having the values available directly from the driver is a nice thing. But just because it is digital, you cannot assume anything about how accurate the values are.

Secondly, there almost never is an energy metering circuit inside a driver. What the driver does, it calculates the consumption. It knows the voltage of the output and it controls the current. So with a simple math it can calculate the power and then integrate it over time to get the energy value. But it remains a calculated value. Still quite useful for many applications, but referring to it as "measured" is a bit misleading.