3.4.8.2 Current Sensor Inputs

PL360MB board features two current sensor inputs for measuring the line and neutral currents. The current sensor used is connected to a 2-point connector (J3 & J19). These differential input lines are routed to an ADC through a configurable filter to accommodate various sensors (Current Transformer (CT), shunt or Rogowski coil). By default, all the inputs have the same layout and filter configuration. Their ground reference is GND node.

Figure 3-22. Current Filter Schematics
Important: By default, PL360MB board is configured to host a CT. The board is equipped with resistors R135, R136, R137 and R138 of 1.62 ohms to fit a 200A max current transformer with 20000:1 turn ratio. Firmware examples for the PL360MB board are configured to host a CT with a current ratio of 1:2000 (split core CT 1:2000 1Arms).
Important: Note that this kit does not provide CT, Rogowski coils, or shunt current sensors.
As previously mentioned, there are various current sensor types compatible with PL360MB board:
  1. CT, e.g., Split Core CT 1:2000 1 Arms. To use a CT, the input network must provide a load (or burden) resistor and a first order low pass filter.
    Info: The load resistor is sometimes integrated inside the CT.

    For CT operation, the filters in Figure 3-22 must be tuned with the following component values:

    • R135, R136, R137 & R138 = Value depends on meter scale current and turn ratio
    • R131, R133, R139 & R141 = 0 Ω 100 ppm tempco
    • R132, R134, R140 & R142 = 3 kΩ, 1%, 100 ppm tempco
    • C98, C107, C115 & C118 = 47 pF / NP0
    • C97, C106, C116 & C119 = Do Not Populate
    • C96, C105, C108 & C117 = 3.3 nF / NP0
  2. Shunt Resistor, e.g., 200A, 50mV Full Scale. To use a shunt resistor, the input network must only provide a first order low pass filter. So, for shunt operation, the filters in Figure 3-22 must be tuned with the following component values:
    • R135, R136, R137 & R138 = Do Not Populate
    • R131, R133, R139 & R141 = 0 Ω 100 ppm tempco
    • R132, R134, R140 & R142 = 3 kΩ, 1%, 100 ppm tempco
    • C98, C107, C115 & C118 = 47 pF / NP0
    • C97, C106, C116 & C119 = Do Not Populate
    • C96, C105, C108 & C117 = 3.3 nF / NP0
  3. Rogowski Coil, e.g., RoCoil Series. To use a Rogowski coil sensor, the input network must provide a second order low pass filter. So, for Rogowski coil operation, the filters in Figure 3-22 must be tuned with the following component values:
    • R135, R136, R137 & R138 = Do Not Populate
    • R131, R133, R139 & R141 = 100 Ω, 1%, 100 ppm tempco
    • R132, R134, R140 & R142 = 3 kΩ, 1%, 100 ppm tempco
    • C98, C107, C115 & C118 = 47 pF / NP0
    • C97, C106, C116 & C119 = 2.2 nF / NP0
    • C96, C105, C108 & C117 = 3.3 nF / NP0