Several types of external (serial interface) A-D converters can be used with LabHelper. In addition, it can read streamed serial data from instruments that provide serial data output (but only one such instrument at a time can be connected). The supported A-D devices are described at these links:
Note for all A-D converters: Modern Macs lack built-in serial ports, so for all A-D converters but the Sable UI3, you'll need a USB to serial converter and driver software (and you may need the latter for the UI3). The units made by Keyspan (now, TrippLite), specifically the USA-19HS, function reliably with LabHelper. Other brands have not worked well, or at all.