RBRcoda OpH

The RBRcoda OpH (Fig. 6) is an optical pH sensor, which measures the response of a pH sensitive foil. It is best suited for mooring applications.

Fig. 6. An RBRcoda OpH sensor

During deployments, always orient the sensor downwards to reduce debris collecting at the aperture and minimise exposure to direct sunlight. Store the sensor dry, in the dedicated storage cap included with the instrument. Rehydrate for 24 hours before deployment. See RBR pH sensor care and maintenance for more information.

pH

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 (Section 7.1).

² Measured at 25°C.

Optical pH measurements require pressure and salinity correction for highest accuracy. When installed on an instrument with pressure and/or a conductivity sensor, these corrections are applied automatically.

If deployed as a standalone sensor or installed on a moored instrument without a pressure or conductivity sensor, manually enter the known absolute pressure and/or salinity value in the table under the Parameters tab in Ruskin.

Temperature

Parameter	Value
Range ¹	-5 to 35°C
Initial accuracy	±0.002°C
Resolution	<0.00005°C
Typical stability	±0.002°C / year
Time constant	<1s

Parameter

Value

Range ¹

-5 to 35°C

Initial accuracy

±0.002°C

Resolution

<0.00005°C

Typical stability

±0.002°C / year

Time constant

<1s

¹ Foil should not be allowed to freeze.

Physical

Parameter	Value
Connector	MCBH-6-MP
Communications	RS-232
Housing	Titanium
Diameter	28mm
Length	~125mm, (~160mm with connector)
Weight	180g in air, 110g in water
Depth rating	Up to 6000m
Sampling rate	24hr to 2Hz
Operating temperature ¹	-5 to 35°C

Parameter

Value

Connector

MCBH-6-MP

Communications

RS-232

Housing

Titanium

Diameter

28mm

Length

~125mm, (~160mm with connector)

Weight

180g in air, 110g in water

Depth rating

Up to 6000m

Sampling rate

24hr to 2Hz

Operating temperature ¹

-5 to 35°C

¹ Foil should not be allowed to freeze.

Power

Parameter	Value
Supply voltage	4.5 to 30V (12V nominal)
Power	75mJ/sample (0.5Hz or slower) 4mA (48mW) (1Hz or faster)
Sleep current	10µA

Parameter

Value

Supply voltage

4.5 to 30V (12V nominal)

Power

75mJ/sample (0.5Hz or slower)

4mA (48mW) (1Hz or faster)

Sleep current

10µA

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

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