A close view of the metering section of a rack PDU under one raking workbench light, the meter body and a small display held to the right of the frame while the left side stays dark

Engineering note · metering

What ±1% metering accuracy means in a rack PDU

±1% describes the meter inside the unit. The 1 grade energy total at a 0.1 kWh step is a separate claim, and it is the one a billing figure is built on.

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Metering: ±1% + 1 digit
Energy total: 1 grade · 0.1 kWh
Voltage scale: 1V · 90V to 350V
Current scale: 0.1A
Readout: OLED at the rack

Parameter set

The figures behind the percentage

The tolerance is one row of the set. The scales, the digits and the window decide what a reading can be used for once it leaves the rack.

Metering and reporting figures published for the series
Item	Published value	What it decides
Metering accuracy	±1%	Current, voltage and active power on a reporting line
Resolution	+1 digit	The last digit of a reading, at the scale it is shown on
Voltage scale	1V · 90V to 350V	The window a voltage reading stays inside tolerance in
Current scale	0.1A	Total per feed, and per outlet on switched builds
Power accuracy	±1% per feed	Which feed a measured load is attributed to
Energy total	1 grade	Whether the total can be used as a billing figure
Energy step	0.1 kWh	The smallest change the total registers
Ambient range	-30°C to 100°C	Temperature at the rack, at 1°C resolution
Humidity	1% to 99%	The second ambient channel beside temperature
Reporting paths	SNMP · Modbus · OLED	Where the same meter value can be read
Ethernet	10/100M × 1	The polling path for meter values
Serial	RS485 × 1	A second path on the same monitoring board
Event store	up to 20,000	Dated entries kept for threshold crossings
Clock	RTC hold	The date written on a stored entry after a power loss
Working voltage	110V~250V AC	The supply the unit is wired to
Frequency	50Hz~60Hz	Supply frequency at the rack
Input current	10A–32A	The feed the unit is ordered against
Output current	10A–16A	The branch rating at each outlet

Read on one poll

What a platform collects from one line

Voltage1V step
Total current0.1A step
Active power±1% per feed
Energy total0.1 kWh step
Outlet currentswitched builds

Mechanism

Where a percentage stops being a percentage

A meter reads the line it is wired to. ±1% says how close that reading sits to the true value; the 1 grade energy total is what makes the sum of those readings usable as a billing figure.

The unit reports total current per feed and, on switched builds, current per outlet. Voltage is read on a 1V scale across a 90V to 350V window, and active power is derived per feed at the same ±1% tolerance. The energy total moves in 0.1 kWh steps on a 1 grade basis, so a billing figure changes in the increments the counter inside the unit already uses. Two lines can only be compared when both are read on the same scale over the same window, and that window belongs to the platform that polls them.

Reads per feed: current · voltage · power
Reads per outlet: current on switched builds
Energy step: 0.1 kWh
Tolerance: ±1% + 1 digit

A 1 grade total is the billing row. It is the figure an invoice can be raised against, at a 0.1 kWh step.
±1% + 1 digit is the measurement row. It states how close one reading sits to the value on the line.
The event log keeps the crossings. Up to 20,000 dated entries, with the clock held through a power loss.

The metering board of a rack PDU inside a dark equipment aisle, its reading window and current transformers lit from the upper left while the racks behind fall out of focus — 1V · 0.1A · ±1% + 1 digit · 0.1 kWh at 1 grade

Reading set

A reading you can reconcile with the log

Each cell is one value on the reporting line, at the scale the unit publishes it on. The same data reaches the rack display and the poller.

Voltage 1V Read across a 90V to 350V window on the reporting line.

Total current 0.1A Summed per feed at ±1% plus one digit.

Active power ±1% Per feed, at the tolerance of the current reading behind it.

Energy total 0.1 kWh Billing-grade total held at 1 grade on every line.

Frequency 50Hz~60Hz The supply band the unit is wired for.

Ambient temperature -30°C Range to 100°C at 1°C resolution on the optional sensor.

Humidity 1%~99% Reported beside temperature from the same sensor.

Stored entries 20,000 Dated threshold records, kept with the clock through a power loss.

Scales above are the published values for the series. A platform that polls a different scale is reading a different register, not a different meter.

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Send the lines you need to measure

Outlet combination, current per feed, metering depth and remote switching. The reply carries the scales for your build and a per-line specification sheet, in English.

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