Experiences with Contrastive Predictive Coding in Industrial Time-Series Classification

Abstract

Multivariate time-series classification problems are found in many industrial settings; for example, fault detection in a manufacturing process by monitoring sensors signals. It is difficult to obtain large labeled datasets in these settings, for reasons such as limitations in the automatic recording, the need for expert root-cause analysis, and the very limited access to human experts. Therefore, methods that perform classification in a label efficient manner are useful for building and deploying machine learning models in the industrial setting. In this work, we apply a self-supervised learning method called Contrastive Predictive Coding (CPC) to classification tasks on three industrial multivariate time-series datasets. First, the CPC neural network (CPC base) is trained with a large number of unlabeled time-series data instances. Then, a standard supervised classifier such as a multi-layer perception (MLP) is trained on available labeled data using the output embeddings from the pre-trained CPC base. On all three classification datasets, we see increased label efficiency (ability to reach a goal accuracy level with less labeled examples). In the low data regime (10's or few 100's of labeled examples), the CPC pre-trained model achieves high accuracy with up to 15x less labels than a model trained only on labeled data. We also conduct experiments to evaluate the usefulness of CPC pre-trained classifiers as base models to start an active learning loop, and find that uncertainty sampling does not perform significantly better than random sampling during the initial queries.