Common causes:

• Completely absorbing peaks
• Electrical ground problems
• Florescent lights
• Failing power supply

Suggestions:

In absorbance mode, noise on top of peaks can create full scale spikes. Check the data in transmittance. View peaks greatly magnified. 0%T is infinite absorbance.

Ground problems: verify complete system is powered from the same circuit, check any new components added for potential ground loop problems. Calculate frequencies and spacing of spikes in Hertz using the following equation:

frequency(Hz) = (scan speed in Hz) • (position of spike in cm^-1) ⁄ (laser frequency in cm^-1)

Many commercial FTIRs have a 632.8nm laser (15798 cm^-1). Harmonics of 60 Hz indicate grounding problems.

Check power supply outputs with oscilloscope. See disclaimer for safety warning. Insufficient voltage or ripple may be present and an indication of failure.