CCLD, stands for Constant Current Line Drive, means the sensor interface using Constant Current Supply.
CCLD from an accelerometer with built-in preamplifier or a microphone preamplifier enables direct connection to an FFT Analyzer without using external amplifier. 2 to 4 mA of CCLD is commonly used.
CCLD offers many benefits;  External amplifier is not required.  Two-wire system cable (coaxial cable etc.) can be used.  Enables cable extension longer than using the other method.  Cable disconnection detecting function can be added.