INSTRUCTION MANUAL 247 Conductivity and Temperature Probes Revision: 3/96 C o p y r i g h t ( c ) 1 9 9 4 - 1 9 9 6 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance The 247-L CONDUCTIVITY & TEMPERATURE PROBE is warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
247 Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. Overview......................................................................1 1.1 EC Sensor .................................................................................................1 1.2 Temperature Sensor ..................................................................................1 2. Specifications ..............
10. Instruction 11 Details................................................9 11. Electrically Noisy Environments............................10 12. Long Lead Lengths Temperature...........................
247 CONDUCTIVITY AND TEMPERATURE PROBES 1. OVERVIEW 247 Probes (247-L and 247W-L) are designed for measuring the electrical conductivity, dissolved solids, and temperature of fresh water with Campbell Scientific dataloggers. They require the use of negative excitation, so they can be used with the CR10(X), 21X, and CR7 dataloggers but not with the BDR301 or BDR320. Electrical conductivity (EC) of a solution is a simple physical property, but measurements can be difficult to interpret.
247 CONDUCTIVITY AND TEMPERATURE PROBES 2.2 EC SENSOR Electrodes: Passivated 316 SS with DC isolation capacitors. Cell constant: Individually calibrated. The cell constant (Kc) is found on a label near the termination of the cable. Temp. Range of Use: Above freezing to 50°C. 4. WIRING The 247s manufactured after January 1, 1994 are connected to a Campbell Scientific datalogger as illustrated in Figure 4-1.
247 CONDUCTIVITY AND TEMPERATURE PROBES FIGURE 4-1. 247 Wiring Diagram 5.2 MEASUREMENT PROGRAMMING. EC Results from Instructions 5 or 6 (chosen automatically as part of the autoranging feature of the following program segment) are processed with Instruction 59 to produce the resistance across the electrodes: Make a preliminary measurement of resistance for autoranging. 01: 01: 02: P6 1 15 03: 1 04: 1 05: 2500 06: 07: 08: 02: 01: 02: 03: 1 -.
247 CONDUCTIVITY AND TEMPERATURE PROBES 11: 01: 02: P6 1 14 03: 1 04: 1 05: 2500 06: 07: 08: 1 -.001 1 Full Bridge Rep 250 mV fast Range (Use 500 mV fast for 21X) IN Chan Excite all reps w/EXchan 1 mV Excitation (Use 5000 mV for 21X) Loc [:Rs ] Mult Offset 12: P95 End 13: P95 End 14: 01: 02: 03: P59 1 1 1 BR Transform Rf[X/(1-X)] Rep Loc [:Rs ] Multiplier (Rf) Subtract resistance errors (Rp) caused by the blocking capacitors (0.005 kΩ) and the cable length (0.000032 kΩ ft-1).
247 CONDUCTIVITY AND TEMPERATURE PROBES 25: 01: 02: 03: P34 3 -.00378 3 Z=X+F X Loc Ct F Z Loc [:Ct 26: P94 Else 27: 01: 02: 03: 04: 05: 06: 07: 08: 09: P55 1 3 3 -.02889 .98614 .02846 0.0000 0.0000 0.0000 Polynomial Rep X Loc Ct F(X) Loc [:Ct C0 C1 C2 C3 C4 C5 28: P95 End ] ] 5.4 CORRECTION OF TEMPERATURE ERRORS The effect of temperature on the sample solution can cause large errors in the EC measurement.
247 CONDUCTIVITY AND TEMPERATURE PROBES 6.4 FIELD CALIBRATION The cell constant is a dimensional number expressed in units of cm-1. The unit cm-1 is slightly easier to understand when expressed as cm·cm-2. Because it is dimensional, the cell constant as determined at any one standard, will change only if the physical dimensions inside the 247 probe change. Error due to thermal expansion and contraction is negligible. Corrosion and abrasion, however, have the potential of causing significant errors.
247 CONDUCTIVITY AND TEMPERATURE PROBES 7. MAINTENANCE Routine maintenance includes thoroughly cleaning the orifice of the 247 probe with the black nylon brush provided and a little soapy water. Rinse thoroughly. 8. ANALYSIS OF ERRORS 8.1 EC MEASUREMENT ERROR 1. Bridge Measurement Error: < 1.0% 2. Calibration Error: bridge measurement: < 0.5% calibration solution: < 1.0% 3. Ionization Error of KCl and Na+ Solutions After Correction: < 2.0%, 0.45 to 7.0 mS cm-1 < 8.0%, 0.005 to 0.
247 CONDUCTIVITY AND TEMPERATURE PROBES 8.2 TEMPERATURE MEASUREMENT ERROR The overall probe accuracy is a combination of the thermistor's interchangeability specification, the precision of the bridge resistors, and the polynomial error. In a "worst case" all errors add to an accuracy of ±0.4°C over the range of -24° to 48°C and ±0.9°C over the range of -38°C to 53°C. The major error component is the interchangeability specification of the thermistor, tabulated in Table 8.2-1.
247 CONDUCTIVITY AND TEMPERATURE PROBES 9. DERIVING A TEMPERATURE COMPENSATION COEFFICIENT 1. Place the 247 in a sample of the solution to be measured. Bring the sample and the probe to 25°C. 2. Enter the example program from Section 5.2 in the datalogger and record Ct at 25°C from Location 3. This number will be C25 in the formula in Step 4. 3. Bring the solution and the probe to a temperature (t) near the temperature at which field measurements will be made.
247 CONDUCTIVITY AND TEMPERATURE PROBES 11. ELECTRICALLY NOISY ENVIRONMENTS AC power lines can be the source of electrical noise. If the datalogger is in an electronically noisy environment, the 107/107B temperature measurement should be measured with the AC half bridge (Instruction 5) with the 60 Hz rejection integration option on the CR10(X) and slow integration on the 21X and CR7 (see Section 13 of the datalogger manual for more information on noise).
247 CONDUCTIVITY AND TEMPERATURE PROBES 13. 247 SCHEMATIC FIGURE 11-1.
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