Profile: Matelect Ltd designs and manufactures precision scientific instruments. The SM-HF scanner system provides a modular way of monitoring multiple specimens and is designed for use in conjunction with the CGM-7 or ACM-1A series of ACPD crack growth monitors. It is modular and can be specified (or expanded) to cover a total of 256 specimen channels. Each module is based on a 4 channel switching unit. Two types of unit exist, the SM1-HF is used for switching the ACPD 0 degree and 90 degree signals, whilst the SM2-HF is used to switch the AC excitation current. Both modules are under the control of an SC1 scan controller module built into both the CGM-7 and ACM-1A, and supplied as standard. The DCM-2 is a modern microprocessor based instrument for measuring crack depth in metals undergoing materials testing. It utilises the pulsed current potential drop method (DCPD) which is an established technique also covered by the ASTM 647 standard. The technique involves passing a constant current through the metal under test and measuring the resultant voltage drop that is created across the specimen. The presence of a growing defect will alter this voltage and by suitable calibration, a measure of the defect depth can be obtained. DCPD is generally regarded as easier to set-up than ACPD.