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WQ201 pH Sensor
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4-20mA Output pH Sensor WQ201
Fully encapsulated electronics 4-20 mA output Marine grade cable with strain relief Stainless steel housing Replaceable pH element
Product Description
The WQ201 pH sensor is a rugged reliable water pH measuring device.
The sensor probe is mounted on 25' of marine grade cable, with lengths up to 500' available upon request.
The pH sensor output is 4-20 mA with a three wire configuration. The electronics are completely encapsulated in marine grade epoxy within a stainless steel housing. The sensor also uses a removable shield and pH element for easy maintenance.
Output: 4-20 mA
Range: 0-14 pH
Accuracy: 2% of full scale
Operating Voltage: 10-36 VDC
Current Draw: 5.5 mA plus sensor output
Warm Up Time: 3 seconds minimum
Operating Temperature: -5c to +55c
Pressure Rating: 0-100 psi
Size of Probe: 1 1/4" diameter x 10" long
Weight: 1 lb.
The pH value of a substance is directly related to the ratio of hydrogen ion (H+) and Hydroxyl ion (OH-) concentrations. If H+ is greater than OH-, the solution is acidic, i.e., the pH value falls in the 0 to 7 range. If the OH- is greater than the H+, the material is basic with a pH value in the 7 to 14 range. If equal amounts of H+ and OH- ions are present, the material is neutral with a pH value of 7.
The pH electrode can be thought of as a battery whose voltage changes as the pH of the solution in which it is inserted changes. It consists of two basic parts: 1) a Hydrogen ion-sensitive glass bulb, and 2) a reference electrode. The special glass of the sensitive bulb has the ability to pass H+ i.e., it is said to be H+ sensitive. This ability allows the H+ inside the bulb to be compared to the H+ outside of the bulb, and a voltage to be developed that is related to the difference. The bulb then is a half-cell that needs a reference voltage in order to function.
The voltage produced by the complete probe is a linear function of pH, generally about 60 mV per pH unit. For example, at 7.00 pH the probe produces zero volts while at 6.00 pH it produces +60 mV. If the voltage had been negative it would indicate that the solution had a value of 8.00 pH.
A buffer solution is a solution with a well-defined pH value and has the ability to resist changes in pH. These characteristics are well suited to the standardization of pH measuring systems. Buffers are available in a wide range of pH values and come either in pre-mixed liquid form or as convenient dry powder capsules. When selecting buffers for use with your particular system, a value should be chosen nearest to that of the sample being measured.