pH

RBR standard instruments support the RBRcoda OpH sensor (Fig. 22) as well as the AMT pH sensors (Fig. 23 and Fig. 24).

Overview

RBRcoda OpH

The RBRcoda OpH performs an optical measurement, producing a temperature-corrected pH reading via thermistor measurements.

Fig. 22. An RBRcoda OpH sensor

Parameter	Value
Measurement range	7 to 9pH_T
Initial accuracy at 35PSU and atmospheric pressure ¹	±0.05pH within pH 7.5–9 ±0.1pH within pH 7–7.5
Resolution	<0.003pH
Time constant ²	<80s

Parameter

Value

Measurement range

7 to 9pH_T

Initial accuracy at 35PSU and atmospheric pressure ¹

±0.05pH within pH 7.5–9

±0.1pH within pH 7–7.5

Resolution

<0.003pH

Time constant ²

<80s

¹ Salinity and pressure dependence is described in the Appendix of the RBR Instrument guide: Sensors.

² Measured at 25°C.

Calibration equations

\[\begin{aligned}pH ={}&c5\,(1 + c4\,(T-20))\,\log_{10}\!\left(\frac{c1\,(1 + c0\,(T-20)) - R}{R - c3\,(1 + c2\,(T-20))}\right)\\[4pt] &+\, c7 + c6\,(T-20) + c8\end{aligned}\]

pH corrected

\[pH_{corrected} = pH - \frac{1}{2}\,c0\left(\frac{\sqrt{S/50}}{1+\sqrt{S/50}} - 0.2791745 - c1\left(\frac{S}{50} - 0.15\right)\right) - c2\,P\]

AMT

The AMT sensors measure hydrogen ion concentration in environmental water, yielding its relative acidity or alkalinity, and thus evaluating water quality. RBR recommends deploying the pH sensor together with the ORP sensor.

Fig. 23. An AMT 1250m pH sensor

Fig. 24. An AMT 6000m pH sensor

Parameter	Value
Accuracy	0.1pH
Resolution	0.01pH
Calibrated range	pH 4 to pH 10
Measurement range	pH 2 to pH 11
Depth rating	1250m/6000m

Parameter

Value

Accuracy

0.1pH

Resolution

0.01pH

Calibrated range

pH 4 to pH 10

Measurement range

pH 2 to pH 11

Depth rating

1250m/6000m

Calibration equation

\[pH_{cor}=(C_0+C_1*V)+X_0*((C_0+C_1*V)-X_1)*(T-X_2)\]