YSI 1001A [605323] Amplified pH Sensor. The YSI 1001A amplified pH and combination pH/ORP sensors have an internal, battery-powered pre-amplifier for use in difficult environments. The amplified sensors are approximately 0.75" (1.91cm) longer than the Model 1001 pH or 1003 pH/ORP Sensors. The available extension adapter attaches to the bulkhead, so longer sensors fit in the probe guard for the Pro1010 and Pro1020 cables (not needed on the Pro Plus Quatro cable).  All YSI flow cells work normally with the new sensors.