Operating instructions - arup-group/pqm-hellebores GitHub Wiki

⚠ Safety instructions

Hazardous voltage is present inside including the measurement PCB. Operate only with cover closed.
Maximum continuous load is 650W (230V). The meter is protected at the IEC inlet assembly with a 3.15A type T ceramic fuse (Schurter part number 0001.2509, RS 789-7794, Mouser 693-0001.2509, Farnell 1360855). Do not replace with a higher rating.
The IEC power connection is subject to pull-out forces so check the fitment. If there is any loose movement at all, you must not use the equipment until this is rectified with compressible adhesive strip at the fixing surfaces.
The insulated enclosure is part of the safety design. Do not breach this enclosure to add wired interfaces eg USB keyboard. Use wireless interfaces only.
The power switch does not isolate the load and in fact the switch contact is bridged with an RC snubber for EMI control: loads must therefore be physically disconnected to isolate.
This research device must be used only by instructed people in a controlled setting. It is NOT suitable for site or field use.
Allow air movement around the device, so that heat can dissipate.

Starting and stopping

Connect input and output IEC leads and apply power. The switch on the box controls output power to the load. After the Raspberry Pi has booted, a launcher should appear on the screen from where you can start the application. Alternatively, find the software under the 'Other' menu category.

Shut down the Raspberry Pi from within the application ('Options') menu, the launcher or the Raspberry Pi menu. To avoid SD card corruption, wait for the green LED to stop flashing on the rear of the Raspberry Pi, approximately 5 seconds after the screen goes dark. Switch off the power at the socket outlet.

Operating modes

Waveform mode

The meter will start in a waveform capture and display mode. You can display up to four different time-correlated waveforms: voltage, current, power and earth leakage current. The on/off selection of waveforms and the vertical and horizontal scales are available on the 'Vertical' and 'Horizontal' controls.

If you want to freeze the image on the display, use the 'Start/Stop' control.

To change the waveform alignment/trigger point, use the 'Trigger' control.

You can disable the trigger entirely by selecting 'Free run': successive waveform updates will be displayed with no synchronisation. When the time axis is a multiple of mains cycle periods, you can directly observe drift of network frequency: at exact frequency the display will be steady, otherwise the waveform will appear to process either leftwards (frequency high) or rightwards (frequency low).

In 'Inrush' mode the meter will automatically stop when a current threshold is reached, thus allowing inrush events (power switch-on) to be observed.

Multimeter mode

Use the 'mode' button to switch to multimeter mode. The software will analyse a 2 second buffer of sample readings and update the display every 1 second.

Measurements include: RMS voltage, RMS current and RMS earth leakage current, instantaneous power, VAR and VA, power factor, crest factor, total harmonic distortion (V and I), frequency, cumulative Wh, VARh and VAh. The multimeter also tracks maximum and minimum extrema of several measurements.

The hardware has two current ranges, 'low' and 'full' range. A warning indication will show up if you are in low range. The low range provides better resolution at very low levels of load, which can be useful for quiescent/standby power measurements. However if instantaneous current exceeds 0.4A then the ADC channel will saturate. The 'full' range should therefore be used for the majority of measurements.

Multimeter calculations including cumulative measurements continue regardless of the display mode. Cumulative measurements and max/min extrema can be cleared using controls on the 'Clear' button.

Harmonic voltage mode

Individual harmonic voltages are displayed from h0 (DC) through to h50. The software will analyse a 1 second buffer of sample readings and update the display every 1 second.

Harmonic magnitudes are displayed as a percentage of the RMS voltage of the system. In the internal FFT analysis, harmonic frequency bins are approximately 1 Hz wide. The appropriate bin for each harmonic frequency is determined dynamically based on the measured fundamental frequency of the system.

Harmonic current mode

Individual harmonic currents are displayed from h0 (DC) through to h50.

As per harmonic voltage display, the harmonic current magnitudes are displayed as a percentage of the RMS current of the load, and the FFT bin selection is automatic.

Logging

Measurements are cached in a .csv file whenever the power quality meter software is running. The filename includes a number based on the process ID (PID) of the CSV generating program.

The measurement log file is stored in RAMdisk and is not preserved during power down or through a re-boot.

Timestamp correctness depends on the device being network connected and able to access a NTP server to set the clock. New readings are appended to the file at 1 second intervals.

Measurement accuracy can be affected by the interactive selection of 'full range' or 'low range' current measurement modes. For the majority of logging use-cases, make sure you are in full range mode, to avoid saturation.

If the meter is attached to wifi and you know the IP address, you can copy the measurement log file(s) to your computer as follows (scp is available on Windows, Mac, Linux, WSL):

scp [email protected]:/run/shm/pqm-hellebores/*csv .

Your computer has to be on the same wifi network as the meter. You must include the space and the 'dot' (this is the destination, the current working directory on your computer). Alternatively transfer the file via Bluetooth file transfer.

Remote access

You can connect remotely to a shell on the Raspberry Pi using SSH.

ssh [email protected]

You'll need to read the IP address from the launch screen and enter the password for the pi user at the prompt.

You can also view the display remotely using VNC. For best performance (ie frame rate), try setting picture quality to 'medium' and encryption to 'prefer off'.