A wound therapy system having a wound dressing for treating a wound includes a sensor that measures a pH level at a wound area. The sensor has a circuit that includes a first electrode and one or more second electrodes. The first electrode has a changeable conductivity that changes according to a hydrogen ion concentration level. The one or more second electrodes are configured with a fixed conductivity that does not change with the hydrogen ion concentration level. The first electrode is coated with a porous protective membrane formed from a sulfonated and/or carboxylated copolymer.