Legacy Direct Current Potential Difference (DCPD) System
The FTA Reversing DC Potential Difference System is designed to provide the precise current and amplifier stability necessary for the reversing DC potential difference method of monitoring crack length. Custom manufactured at LTI, the system is intended to be used in conjunction with the FTA ADwin-Gold and FTA control testing software, which synchronizes current reversing and voltage measurement. Crack length precision is usually on the order of 0.001 inches or less for typical fracture mechanics specimens and conditions.
The FTA programmable linear DC power supply has a current rating of 20 amps and a voltage rating of 5 volts. Solid-state polarity-reversing relays have been internally integrated and are controlled by two digital logic signals from the ADwin-Gold. Polarity reversing has two distinct advantages over pulsed (on/off) current control. First, for a given constant current, the magnitude of the voltage difference is twice the difference obtained with pulsed current control. Second, the durability of the DC power supply is enhanced since the current output remains constant and the switching transients are minimal.
The FTA true differential amplifier offers up to 6 channels for active and reference probes. The low-level signals are conditioned and filtered using Ectron model 428-O precision differential amplifiers to provide a maximum gain of 2,500x. Unique features include manual or auto-zero of the input signal and a 4 Hz filter bandwidth. The amplifier offers isolated true differential input, excellent temperature stability and immunity to EMI/RFI noise.
LTI manufactures high-quality PD cables to be used with our DCPD systems, available in standard 6’, 10’, and custom lengths. The cables are fully shielded and connect from the test specimen to the high-precision differential amplifier.