The Sea-bird Electronics SBE 18 pH sensor can be integrated in the SBE 19 plus V2 CTD to measure pH to a depth of 1,200 meters. Simple to install, maintain and calibrate, this sensor measures pH to an accuracy of 0.1 pH with a quick time response.

SBE 18 must always be mounted with the pH probe in a vertical orientation, as shown in the spec sheet. A right angle probe configuration is typically required for applications where the CTD is mounted horizontally (for example, in an extension stand below an SBE 32 Carousel Water Sampler) and the SBE 18 is mounted to the CTD.