CSIM11-L pH Probe

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1. Why is silver used for the wire in the reference electrode of a pH sensor?

   Silver is the best electrical conductor of all the metals because it has the lowest electrical resistance. The silver wire, coated in silver chloride, is relatively insensitive to changes in temperature. 

2. How does a reference electrode in a pH sensor become contaminated?

   A reference electrode can become contaminated when poisoning ions such as lead, iron, chrome, cyanide, or sulfide enter the reference electrode and react either with the silver wire or with the electrolyte solution.

   The contamination may not become apparent until the silver-chloride coating is completely dissolved and the electrical potential from the reference electrode has changed greatly. If this occurs, the reference electrode must be replaced.

3. When is cleaning or calibration needed for a pH sensor?

   Cleaning and/or calibration may be required when the measurements are scattered, drifting occurs, or there is physical evidence of fouling. Measurements for pH must be monitored regularly to check for scattering. However, just because the results are scattered does not necessarily indicate the need for an adjustment. For example, there may be a change in the water source that causes the scattering. As a sensor ages, however, the scattering of the measured values tends to increase.

   To check the performance of a pH sensor, use it to measure a buffer solution in the correct range. If the value returned is within the specified range, the sensor does not need to be calibrated.

4. What is a multipoint calibration, and when is it done on a pH sensor?

   In the event that both alkaline and acidic sample solutions are measured using a single pH sensor, a multipoint calibration is done using three buffer solutions. As in the two-point calibration, the first buffer solution has a 7.0 pH. The second buffer solution should be near in pH value to either the acidic or alkaline sample solution, and the third buffer solution should be near in pH value to the other.

5. Where are the available cable termination options listed for a particular sensor?

   Not every sensor has different cable termination options. The options available for a particular sensor can be checked by looking in two places in the Ordering information area of the sensor product page:

   • Model number
   • Cable Termination Options list

   If a sensor is offered in an –ET, –ETM, –LC, –LQ, or –QD version, that option’s availability is reflected in the sensor model number. For example, the 034B is offered as the 034B-ET, 034B-ETM, 034B-LC, 034B-LQ, and 034B-QD.

   All of the other cable termination options, if available, are listed on the Ordering information area of the sensor product page under “Cable Termination Options.” For example, the 034B-L Wind Set is offered with the –CWS, –PT, and –PW options, as shown in the Ordering information area of the 034B-L product page.

   Note: As newer products are added to our inventory, typically, we will list multiple cable termination options under a single sensor model rather than creating multiple model numbers. For example, the HC2S3-L has a –C cable termination option for connecting it to a CS110 instead of offering an HC2S3-LC model. 

6. What are the different cable length choices available for Campbell Scientific sensors?

   Most Campbell Scientific sensors are available as an –L, which indicates a user-specified cable length. If a sensor is listed as an –LX model (where “X” is some other character), that sensor’s cable has a user-specified length, but it terminates with a specific connector for a unique system:

   • An –LC model has a user-specified cable length for connection to an ET107, CS110, or retired Metdata1.
   • An –LQ model has a user-specified cable length for connection to a RAWS-P weather station.

   If a sensor does not have an –L or other –LX designation after the main model number, the sensor has a set cable length. The cable length is listed at the end of the Description field in the product’s Ordering information. For example, the 034B-ET model has a description of “Met One Wind Set for ET Station, 67 inch Cable.” Products with a set cable length terminate, as a default, with pigtails.

   If a cable terminates with a special connector for a unique system, the end of the model number designates which system. For example, the 034B-ET model designates the sensor as a 034B for an ET107 system.

   • –ET models terminate with the connector for an ET107 weather station.
   • –ETM models terminate with the connector for an ET107 weather station, but they also include a special system mounting, which is often convenient when purchasing a replacement part.
   • –QD models terminate with the connector for a RAWS-F Quick Deployment Station.
   • –PW models terminate with the connector for a PWENC or pre-wired system.
7. What are the different cable termination options available for Campbell Scientific sensors?

   Many Campbell Scientific sensors are available with different cable termination options. These options include the following:

   • The –PT (–PT w/Tinned Wires) option is the default option and does not display on the product line as the other options do. The cable terminates in pigtails that connect directly to a datalogger.
   • In the –C (–C w/ET/CS110 Connector) option, the cable terminates in a connector that attaches to a CS110 Electric Field Meter or an ET-series weather station.
   • In the –CWS (–CWS w/CWS900 Connector) option, the cable terminates in a connector that attaches to a CWS900-series interface. Connection to a CWS900-series interface allows the sensor to be used in a wireless sensor network.
   • In the –PW (–PW w/Pre-Wire Connector) option, the cable terminates in a connector that attaches to a prewired enclosure.
   • In the –RQ (–RQ w/RAWS Connector) option, the cable terminates in a connector that attaches to a RAWS-P Permanent Remote Automated Weather Station.

   Note: The availability of cable termination options varies by sensor. For example, sensors may have none, two, or several options to choose from. If a desired option is not listed for a specific sensor, contact Campbell Scientific for assistance.

8. How is a pH sensor calibrated?

   The recommended calibration method listed in a specific pH sensor’s instruction manual should be followed to guarantee the best results. Calibration must be performed correctly to ensure accurate and repeatable measurements. Before performing calibration, the pH sensor should be cleaned.

   Calibration is commonly done using a known-value pH solution called a buffer. The buffer solution is formulated to resist pH changes caused by external contaminants. However, the pH of the buffer solution changes as the temperature changes. To compensate for this, manufacturers list the pH of the buffer solution at various temperatures on the buffer solution’s bottle so that the correct value for calibration is selected.

   The most common calibration method is a two-point calibration using two buffer solutions. Each buffer solution has known and accurate pH values at different temperatures. The buffers used should be based on the normal measurement range that the pH sensor operates in for the application. One buffer solution should have a 7.0 pH. The second buffer solution should have a pH that is near the expected pH value of the sample solution.