The CT-BOX is a measuring system for the measurement of direct and alternating currents with high accuracy and precision, whereby the measured values are made available in various digital formats. The CT-BOX system was developed for use with CARNels current transformers, which enable measurements of currents up to kA.
A load resistor and a conditioning network are integrated in the system, via which a temperature-stabilized 24-bit ADC digitizes the measured value from the current transformer. Overall, this arrangement achieves a temperature dependency of less than 1 ppm / K. With the digital circuit and the ADC, a calibrating measurement is carried out in order to compensate for non-ideal behavior. This achieves a current measurement accuracy of 0.005% (full scale). The ADC sampling frequency can be configured up to 100 kHz, which can detect high-frequency current peaks and fast current transients.
Current measurement values can be triggered by different trigger modes:
- By an external LVTTL or TTL signal (hardware trigger)
- By a remote command that is sent to the digital interface (software trigger)
- Through device-internal setting of the sampling period and the acquisition period (mixed trigger)
The time stamp, the current measured values and the outside temperature values are stored in a microSD flash memory, which also enables long-term data acquisition.
The SD flash memory can either be read via Ethernet, USB or RS-232 interfaces, or it can be removed from the system and plugged into another device to download the content.
If necessary, a temperature sensor can be connected to the rear of the system in order to measure and save external temperature values.
The device display shows the current measured values and other settings. A configurable alarm output can be used to signal an external device when a preset current threshold is exceeded. An integrated auto-zero function enables the compensation of offset measuring currents.
The CT-BOX can be connected directly to the power supply and has a low-noise AC / DC power supply with a nominal output voltage of +/- 15 V. This integrated power supply supplies the active current transformer and thus offers the required measuring accuracy of <0.001% at 100 kHz bandwidth.
The very compact design (1 height unit and a width of 9 inches) allows the device to be used in the laboratory or two devices in a 19 “rack. Appropriate brackets can be ordered separately.
Note:
- The CT-Box and the CT-100-C current transformer are calibrated together to achieve high accuracy.
- Measurements are possible with another current transformer of the same nominal current class, however the accuracy is not specified here.