Editing PH meter (section)

==Types of pH meters==
[[Image:2009-03-30 Red pH meter reads 4.96.jpg|thumb|right|A simple pH meter]]
[[Image:Soil pH meter.jpg|thumb|right|[[Soil pH]] meter]]

In general there are three major categories of pH meters.  Benchtop pH meters are often used in laboratories and are used to measure samples which are brought to the pH meter for analysis.  Portable, or field pH meters, are handheld pH meters that are used to take the pH of a sample in a field or production site.<ref>{{cite web |title=What is a pH Meter and How Does it Work? |url=https://www.mt.com/global/en/home/products/Laboratory_Analytics_Browse/pH-meter.html#custom4 |publisher=Mettler-Toledo LLC |access-date=21 July 2021}}</ref>  In-line or in situ pH meters, also called pH analyzers, are used to measure pH continuously in a process, and can stand-alone, or be connected to a higher level information system for process control.<ref>{{cite web |title=A guide to pH Measurement Theory and Practice |url=https://www.mt.com/global/en/home/library/guides/process-analytics/ph-measurement-guide.html |publisher=Mettler-Toledo LLC |access-date=21 July 2021}}</ref>

pH meters range from simple and inexpensive pen-like devices to complex and expensive laboratory instruments with computer interfaces and several inputs for indicator and temperature measurements to be entered to adjust for the variation in pH caused by temperature. The output can be digital or analog, and the devices can be [[battery-powered]] or rely on [[line power]]. Some versions use telemetry to connect the electrodes to the voltmeter display device.<ref name="Galster" />{{rp|197–215}}

Specialty meters and probes are available for use in special applications, such as harsh environments<ref name="Olson">{{cite web|last1=Olson|first1=Vickie|title=How to Select a pH Sensor for Harsh Process Environments|url=http://automation.isa.org/2015/04/how-to-select-a-ph-sensor-for-harsh-process-environments/|website=automation.isa.org|publisher=International Society for Automation|access-date=31 March 2017|date=2015-04-15}}</ref> and biological microenvironments.<ref name="MMB2010" /> There are also holographic pH sensors, which allow pH measurement [[Colorimetry (chemical method)|colorimetrically]], making use of the variety of [[pH indicators]] that are available.<ref>{{cite journal |author1=AK Yetisen |author2=H Butt |author3=F da Cruz Vasconcellos |author4=Y Montelongo |author5=CAB Davidson |author6=J Blyth |author7=JB Carmody |author8=S Vignolini |author9=U Steiner |author10=JJ Baumberg |author11=TD Wilkinson |author12=CR Lowe |title=Light-Directed Writing of Chemically Tunable Narrow-Band Holographic Sensors |journal= Advanced Optical Materials |volume=2 |issue=3 |pages=250 |year=2013 |doi= 10.1002/adom.201300375 |s2cid=96257175 |url=https://www.repository.cam.ac.uk/handle/1810/293246 }}</ref> Additionally, there are commercially available pH meters based on [[ISFET|solid state electrodes]], rather than conventional glass electrodes.<ref name="solidstate">{{cite web|title=pH Electrode|url=http://www.ph-meter.info/pH-electrode-solid-state|website=pH-meter.info|access-date=30 March 2017}}</ref>