The new DLT current transducers from NK Technologies are single range, take less panel space in combiner or re-combiner boxes, and produce a 4-20 mA signal through a two wire loop, using nominal 24VDC in series with the output. As with all loop powered signals, they can be converted to 1-5 VDC or 2-10 VDC by the addition of a field installed resistor across the controller input terminals. The design saves time and cabling costs, as just two wires are used rather than four with previous designs.
Perfect for photovoltaic panel monitoring, at the panel, string or array level. Small size allows for placement inside combiner boxes, and the extended temperature range means a lower need for cooling of the control system.
Place wire to be monitored through sensor aperature. Care should be taken to ensure current ? ow is in accordance with any directional arrows on sensor and as noted in the ? gure, above right.
DLT Series transducers work in the same environment as motors, contactors, heaters, pull-boxes, and other electrical enclosures. They can be mounted in any position or hung directly on wires with a wire tie. For optimal performance, ensure unit has been energized for a period of 20 minutes prior to sensing operation.
Monitoring PV Arrays:
The current produced by a photovoltaic module or array can be easily monitored by using the DLT series current sensors over the conductor exiting the collectors. A simple two-wire connection, powered by 24 VDC nominal in series with the sensor output, and the sensor will produce a signal in real time that is directly proportional to the current being produced.
If a single cell fails, or a module quits operating properly, the current output will drop, and the current sensor will reflect the change. Safer and more stable than shunts, non-contact current sensors are a simple answer to measuring DC current at any point in the PV system.
4-20 mA Output
Notes: Fingersafe captive screw terminals. 12–22 AWG solid or stranded. Observe polarity.
The current loop is powered by an external source. The connection diagram on the right. Maximum loop impedance is 500 Ω.
Ensure the direction of monitored current is the same as the direction shown on the diagram. The unit will not operate properly if the current is opposite the direction of the arrow.
Wiring & Mounting Information
Connect the negative from the power sup- ply to the negative of the load (panel meter, PLC, etc.). Connect the positive from the power supply to the positive terminal of the sensor. Connect the negative terminal of the sensor to the positive or input of the load. Or, connect the postive of the power supply to the positive input of the load, negative of the supply to the negative of the sensor, and the positive of the sensor to the negative of the load. Either will work.
Loop Voltage Requirements:
DLT Series transducers feature factory calibrated ranges.
1. Output Signal Too Low
- Determine the normal operating amperage of monitored circuit
- Select the model with a range that is equal to or slightly higher than the normal operating amperage.
2. Output Signal is always at maximum
- There may be current present, but lower than expected. Check primary current with a meter.
- Power supply is inadequate. Check power supply. Make sure it is of sufficient voltage with all loads at maximum. DLT Series consumes less than 1 VA.
- Output load too high. Check output load, be sure it is no more than 500 Ω.
3. Sensor has no output
- There may be current of a higher level than the sen- sor range. Replace with a sensor having a higher range.
- Polarity is not properly matched. Check and correct wiring polarity.
- Monitored load is not DC or is not on. Check that the monitored load is DC and that it is actually on.