Frequently Asked Questions
Click on the topic headings to read answers to questions in that section.
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What’s the difference between displacement and apparent power factor?
Displacement power factor is the ratio of the fundamental (60 Hz) real power to apparent power. Apparent power factor is a ratio of total real power (including harmonic component) to apparent power.
Can I use the software to assist in verifying a current transformer connection?
Yes. If no current transformer is connected to a channel that is turned on, then a non-zero reading will be displayed. If the CT is connected but shows a ‘0’ for a value, then the CT is probably connected but the monitored load is turned off. On the other hand if a constant value for current is displayed, a CT wire may have come off of the logger.
How can there be a Power Factor of .87 on a 3-Phase Delta lighting load?
The line currents in a delta are shifted 30° compared to the line-line voltage. One line current will be shifted +30° and the other line current shifted -30° when compared to the line-line voltage. Since power factor is COS(theta), then COS 30° = .866. This will be true for the hardware channels. If the power sum channel (5 or 6) is used, the power factor for the whole load should be as expected.
Is the battery on my DENT ELITEpro/DATApro/SMARTlogger rechargeable?
No. These DENT loggers have single-use Lithium cell batteries that cannot be recharged and should be disposed of properly. Please contact DENT Instruments for replacement batteries.
Why am I seeing negative Watts on one phase of a 3-Phase Delta system?
The line currents in a delta are shifted 30° compared to the line-line voltage. When connected to a load that has a PF of <.5 (>60°) (e.g. a motor not fully loaded) one line current becomes shifted >90° (30° +>60°) when compared to the line-line voltage. The other phase is shifted >30° (-30° + >60°). The COS of an angle >90° is negative, therefore WATTs = COS(theta)VA is negative for that phase. However, as with the power factor the sum of the watts in a delta should be positive. If not, check the CT orientation, one or both may be reversed. Also check to make sure the CT’s are referenced to the correct line voltages.
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