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MCC 128 input impedance question



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2 MΩ is considered high source impedance which causes measurement errors. The MCC 128 channels share a single A/D converter, each taking a turn. When a channel is selected, a small charge from the previous channel is transferred. If all the channels are connected to low-impedance sources (< 100), the charge dissipates, letting the source charge the input to the real value. However, a high-impedance source cannot dissipate the charge and gets added or subtracted from the real value.  If the current transformer is the only channel being read, it doesn't matter. The current sensor outputs a significant signal (0-10v), and depending on the other channels, the error caused by the high impedance may be small enough to ignore. 

Best regards,

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