Modes of Operation
Three modes of operation can be selected for measurement purposes with the MODE command.
OSCILLOSCOPE (OSC) Mode
OSC mode allows obtaining measurements at the acquisition rate of 100 kHz (the ADC sampling rate), thus making it possible to acquire high-frequency components and fast current transients, as well as to perform an average over a large number of samples (thus reducing the output data rate).
In this mode the data can be read using only the Ethernet communication interface and data saving to the SD card is not allowed. The measurements are sampled at 100 kHz; if such speed is not needed, the output data rate can be reduced down to 1 Hz by averaging the fixed 100 kHz samples, using the TS command. Data is streamed out using the UDP protocol.
DATA-LOGGER (DLOG) Mode
DLOG mode is dedicated to long-time acquisitions with a slower output data rate. The current measurements can be read over the communication interface and/or stored on the connected SD card. Optionally, it is also possible to read and/or store the temperature of the DCCT and/or the external temperature (measured with an external sensor attached to the D-SUB DA-15S (female) connector on the back of the CT-BOX unit – see ACQT).
In this mode of operation, the output data frequency can be set in the range 0.1 Hz – 10 Hz using the FREQ command. In this mode an average is always computed.
DIGITAL-MULTIMETER (DMM) Mode
DMM mode allows the CT-BOX to operate as a digital multimeter, providing DC, AC and ACDC (true RMS) measurements. Samples are always acquired at a fixed rate of 100 kHz. Each output value is computed over a measurement window whose length is set by two commands (DMM:FREQ and DMM:NOP):
Window length = DMM:NOP / DMM:FREQ
Output data frequency = DMM:FREQ / DMM:NOP
With DMM:FREQ = 47 – 63 Hz and DMM:NOP = 1, 10, 20 or 100, the output data frequency ranges from 0.47 Hz to 63 Hz.
For example, DMM:FREQ:50 and DMM:NOP:10 give a 200 ms window (20 000 samples) and one output value every 200 ms (5 Hz).
Because the window always covers a whole number of periods, components at DMM:FREQ and its harmonics
are rejected (DC) or integrated without partial-cycle errors (AC, ACDC).
DMM:DC
Output data is the mean of the samples in the window. Set DMM:FREQ to the power grid frequency to reject
grid noise and its harmonics. DMM:NOP is equivalent to the NPLC (Number of Power Line Cycles) setting of a
conventional multimeter: higher values give lower noise but a slower output rate.
DMM:ACDC
Output data is the true RMS of the samples in the window, including both DC and AC components.
Set DMM:FREQ to the frequency of the measured signal (47 – 63 Hz) so the window spans an exact number of
signal periods. DMM:NOP sets how many periods the window covers.
DMM:AC
Output data is the RMS of the samples after the mean value over the same window has been removed,
i.e. only the AC component is measured. DMM:FREQ and DMM:NOP work as in ACDC mode.
Comparison Between the Three Modes
Parameter |
OSC mode |
DLOG mode |
DMM mode |
|---|---|---|---|
Sampling frequency (fixed) |
100 kHz |
100 kHz |
100 kHz |
Output data frequency |
1 Hz – 100 kHz |
0.1 Hz – 10 Hz |
0.47 Hz – 63 Hz |
Data representation |
Binary |
ASCII |
ASCII |
Representation length |
Fixed |
Variable |
Variable |
Acquisition values |
Index, status, current |
Index, status, current, 2 optional temperatures |
Index, status, current |
Saving data to the SD card |
Not allowed |
Allowed |
Allowed |
Communication interfaces |
Ethernet only (UDP stream) |
Ethernet, USB 2.0, RS-232 |
Ethernet only (TCP/IP) |
Commands per Mode
Most CT-BOX commands apply in all three modes. The following commands apply only in some modes:
Mode |
Mode-specific commands |
|---|---|
OSC |
|
DLOG |
|
DMM |
Except for ACQT, a command that only changes a setting (for example FREQ,
TS or DMM) is accepted in every mode, so all settings can be prepared
before switching mode with MODE; the setting
takes effect only in the mode(s) it applies to. The SD commands are also
accepted in every mode, but data is saved to the SD card only in DLOG and DMM
modes. GET is rejected with NAK:5 in DMM mode, and ACQT in OSC and DMM
modes. A TRG submode selected outside its modes is rejected with NAK:27.
The commands are documented grouped by purpose in Commands. The applicable mode is stated at the top of each command page and summarized in the Command Table Summary.