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What's pH ?

The pH, for definition, is the negative logarithm of  H+ ion concentration in a solution; mathematically speaking : pH =- log[H+]
The values ran from 0 to 7 for acidity and from 7 to 14 for basicity. 

The pH measurement is important in every field of application like food industry, pharmaceutical, cosmetics, galvanic, etc. 

pHmeters are digital instruments used to measure the pH value in a product or an aqueous solution. 

The pH measurement chain consists of:

   -  an indicator with digital display

   -  pH sensor ( pH electrode )

   -  connection cable for pH electrode 

Since the pH measurement is influenced by temperature variation, to correct this type of alteration, mostly of pHmeters are completed with temperature probe to compensate the electrode's answer.  

pHmeters can be portables or bench-top instruments.

The mainly differences are in power supply and dimensions.

Portables are smaller and with battery power supply.

Bench-top ones have bigger display, useful to work in laboratory and often with arm stand.