PQube User Manual 2.1
Page 48 of 113
Additional Channels Available With Optional Current Module
Mains Current Measurements
There are two optional types of current inputs into your PQube.
The optional CT4-50A current sense module allows you to measure up to 50 amps directly (limited
by insulated conductor diameter). Simply pass the mains conductors through the CT4 module. The
CT4-20A current sense module is identical, but rated at 20A.
The optional XCT4-1A and XCT4-5A current transformer interface modules work with external
current transformers, with 1-amp or 5-amp secondaries.
The optional XCT5-0.333V, XCT5-01V, XCT5-05V, and XCT5-10V current transformer interface
modules work with external current sensors, with 0.333-volt, 1-volt, 5-volt, or 10-volt outputs.
The crest factor for all PQube current modules is 3.5 (in other words, a PQube current module that
is rated at 100 amps can measure instantaneous current up to ±350 amps).
CT4 Module (attached to a PQube)
XCT4 Module (attached to a PQube)
Full-Scale Current and Noise with Current Transformers
Your full-scale current is the CT Ratio multiplied by the full scale of your external current sensing
module (XCT4 or XCT5). For example, if you are using 100A:0.333V current transformers with an
XCT5-0.333V module, your full scale current would be 100/0.333 multiplied by 0.333, or 100A.
Your PQube uses this value to determine the full scale power.
With no load, you may experience small noise levels that are roughly 0.5% of full scale current.
This noise is extremely small relative to full scale current. But with large CT ratios, you may see a
significant noise value on the PQube display. This does not affect your power (kW) readings, since
your PQube will zero out the reading if the kW reading is below 1% of full scale power.
You can choose to force the current reading to read zero on the display if the current is below a
specified threshold. In the [Measurement_Setup] section of your Setup.ini file, find the
Minimum_Current_Display_In_Percent_Of_Rated_Current tag. By default, this value is 0. Any nonzero
number here will set the current to zero when it is less than the value specified here, as well as the
corresponding VA, Power, and other current-dependent parameters. 1% is a recommended
starting point if you want to use this feature.
Note that at 10% of full scale or higher, noise becomes a non-factor.
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