BSL PRO Software Guide - Biopac

290 Part ECalibrationBIOPAC transducers can provide accurate “relative” measures without calibration.For example, the voltage output of the EDA/GSR transducer (SS3LA) will change by 1 mV given achange of 10 micro Mhos across the electrode(s) connected to the transducer.For accurate “absolute” measurement, the voltage output of the transducer must be correlated exactly toa physical parameter (such as air flow) and must adjust for temperature, pressure, humidity, andorientation (gravity effects)—all of which can vary greatly. Factors beyond the transducer’s accuracy alsoinfluence “absolute” measurement, such as connections in the system or to the subject. While theMP36/35 is a very sensitive, DC stable acquisition unit, too many factors influence true “absolute”measurement to achieve it without calibration.Calibration GuidelinesCalibration is required if ALL of the following are true:1. Precise, absolute, measurements are required.“Precise” is considered better than 5% accurate; some transducers may provide better than 5%accuracy without calibration.“Relative” measurements are often acceptable. Measurements on humans can vary so greatlyfrom person to person that in most cases a “relative” measure of change is sufficient.For example, when measuring EDA with the SS3LA, the preset: “Electrodermal Activity (GSR)Change” is often used and no calibration is required.2. The transducer will be plugged into an Analog Input channel.3. Communication between the MP36/35 and transducers that can be plugged into the “I/O Port” onthe back of the MP36/35 (such as the noninvasive blood pressure cuff) occurs serially; since A/Dconversion is not used, readings will directly match the output of the connected device.4. The operational bandwidth of the transducer extends down to 0 Hz (DC - see page 789 for details).When an AC Coupled Preset is selected for a transducer, “relative” measurements are taken andcalibration is not required.Visit the online support center at www.biopac.com