KAD/ADC/115/NRTD

The KAD/ADC/115/NRTD provides independent excitation for up to 16 channels and is intended for Negative Resistance Temperature Detector (NRTD) type sensors such as the Cernox family of sensors from Lake Shore Cryotronics, Inc.

Each channel has a separate programmable digital filter and A/D converter.

At the heart of the KAD/ADC/115/NRTD is a hard-wired state-machine that oversamples all channels at a rate between 100ksps and 200ksps and digitally filters any noise above the user-programmable cutoff frequency. This is achieved using cascaded, half-band, finite-impulseresponse filters followed by an 8th order Butterworth Infinite-ImpulseResponse (IIR) filter with a default cutoff point set at one quarter of the sampling frequency (fc = fs / 4).

All signals are sampled simultaneously. Thus, when several channels are sampled at different sampling rates, at the start of an acquisition cycle, all channels are aligned.

The excitation current through the NRTD is kept constant. As the resistance changes, the voltage across the NRTD (and hence as seen by the amplifier) changes.

A linearization table for each channel can be used to compensate for nonlinear sensors or to fine-tune gain and offset.