Campbell Scientific 247-L User Manual

INSTRUCTION MANUAL

247 Conductivity and

Temperature Probes

Revision: 3/96

Copyright (c) 1994-1996

Campbell Scientific, Inc.

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 nor mal use and service for twelve (12) months from date of
shipment unless specifi ed 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.
The customer shall assume all costs of removing, reinstalling, and shipping
defective products to CAMPBELL SCIENTIFIC, INC. CAMPBELL
SCIENTIFIC, INC. will return such products by surface carrier prepaid. This
warranty shall not apply to any CAMPBELL SCIENTIFIC, INC. products
which have been subjected to modification, misuse, neglect, accidents of
nature, or shipping damage. This warranty is in lieu of all other warranties,
expressed or implied, including warranties of merchantability or fitness for a
particular purpose. CAMPBELL SCIENTIFIC, INC. is not liable for special,
indirect, incidental, or consequential damages.

Products may not be returned without prior authorization. The following
contact information is for US and International customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle repairs
for customers wi thin their territories. Please visi t www.campbellsci.com to
determine which Campbell Scientific company serves your country. To obtain
a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone [phone]. After an applications engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container.
CAMPBELL SCIENTIFIC's shipping address is:

CAMPBELL SCIENTIFIC, INC.

RMA#_____
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CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

247 Table of Contents

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1. Overview......................................................................1

1.1 EC Sensor .................................................................................................1

1.2 Temperature Sensor..................................................................................1

2. Specifications .............................................................1

2.1 Probe.........................................................................................................1

2.2 EC Sensor .................................................................................................2

2.3 Temperature Sensor..................................................................................2

3. Installation...................................................................2

3.1 Site Selection ............................................................................................2

3.2 Mounting...................................................................................................2

4. Wiring ..........................................................................2

5. Programming ..............................................................2

5.1 Programming Overview............................................................................2

5.2 Measurement Programming......................................................................3

5.3 Correction of Ionization Errors in EC Measurement ................................4

5.4 Correction of Temperature Errors.............................................................5

5.5 Output Processing.....................................................................................5

6. Calibration...................................................................5

6.1 Conversion Factors...................................................................................5

6.2 Typical Ranges .........................................................................................5

6.3 Factory Calibration...................................................................................5

6.4 Field Calibration.......................................................................................6

7. Maintenance................................................................7

8. Analysis of Errors.......................................................7

8.1 EC Measurement Error.............................................................................7

8.2 Temperature Measurement Error..............................................................8

9. Deriving a Temperature Compensation

Coeffecient.......................................................................9

i

10. Instruction 11 Details................................................9

11. Electrically Noisy Environments............................10

12. Long Lead Lengths Temperature...........................10

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. This manual instructs the
user how to make EC measurements with the

247. Accuracy specifications apply to
measurements of EC in water containing KCl,
Na
calibration compounds, and to EC not yet
compensated for temperature effects.

Statements made on methods of temperature
compensation or estimating dissolved solids are
included to introduce common ways of refining and
interpreting data, but are not definitive.
Authoritative sources to consult include the USGS
Water-Supply Paper 1473, The pH and Conductivity
Handbook published by OMEGA Engineering,
physical chemistry texts, and other sources.

1.1 EC SENSOR

The EC sensor consists of three stainless steel
rings mounted in an epoxy tube as shown in
Figure 4-1. Resistance of water passing

, NaHCO3, and/or NaCl, which are typical

2SO4

through the tube is measured by excitation of
the center electrode with positive and negative
voltage. The two outer electrodes return the
signal to the datalogger.

This electrode configuration eliminates the
ground looping problems associated with
sensors in electrical contact with earth ground.

1.2 TEMPERATURE SENSOR

Temperature is measured with a thermistor in a
three wire half bridge configuration.

2. SPECIFICATIONS

2.1 PROBE

Construction: The probe housing is epoxy with
rounded ends to facilitate installation and removal.

Size: Length 3.125". Diameter 0.75". The
diameter of the weighted 247W-L version with
the stainless steel sleeve is 1.05".

Maximum Cable Length: 1000 ft. The sensor
must be ordered with desired length as cable
cannot be added to existing probes.

Depth Rating: Maximum 1000 ft. In
applications that require probe placement in
well casings, the weighted 247W-L is strongly
recommended.

pH Range: Solution pH of less than 3.0 or greater
than 9.0 may damage the epoxy housing.

SOLDER

SIDE

LAC-2

2292

FIGURE 1-1. 247 Conductivity and Temperature Probe

1

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.
EC Range: Approx. 0.005 to 7.5 mS cm-1.
Accuracy: in KCl and Na2SO4, NaHCO3, and

NaCl standards at 25°C:

±5% of reading 0.44 to 7.0 mS cm
±10% of reading 0.005 to 0.44 mS cm

2.3 TEMPERATURE SENSOR

Thermistor: Betatherm 100K6A1.
Range: 0°C to 50°C.
Accuracy: Error ±0.4°C (See Section 8.2).

3. INSTALLATION

CAUTION: Rapid heating and cooling of the

probe, such as leaving it in the sun and then
submersing it in a cold stream, may cause
irreparable damage.

4. WIRING

The 247s manufactured after January 1, 1994
are connected to a Campbell Scientific
datalogger as illustrated in Figure 4-1.

NOTE: The excitation channel used for EC
must be separate from the one used for
temperature or measurement errors will result.

To make previous versions of the 247 (those
without an orange lead) compatible with the
information in this manual, connect existing

-1

.

-1

.

wires as shown in Figure 4-1. Attach one end
of a short piece of insulated wire to the
excitation channel servicing the black lead and
the other end to the H side of the selected
differential channel (this wire acts as the absent
orange lead). If your probe has a blue lead, it is
no longer needed. Tape the exposed portion to
avoid shorting the sensor.

5. PROGRAMMING

5.1 PROGRAMMING OVERVIEW

Typical datalogger programs to measure the
247 consist of four parts:

1. Measurement of EC and temperature

3.1 SITE SELECTION

The EC sensor measures the EC of water
inside the epoxy tube, so detection of rapid
changes in EC requires that the probe be
flushed continuously. This is easy to
accommodate in a flowing stream by simply
orienting the sensor parallel to the direction of
flow. In stilling wells and ground wells,
however, diffusion rate of ions limits the
response time.

3.2 MOUNTING

The epoxy housing and sensor cable are made
of water impervious, durable materials. Care
should be taken, however, to mount the probe
where contact with abrasives and moving
objects will be avoided. Weighting to facilitate
installation in wells is provided by the stainless
steel sleeve on the 247W-L. Strain on cables
can be minimized by using a split mesh strain
relief sleeve on the cable, which is
recommended for cables over 100 ft. The
strain relief sleeve is available from Campbell
Scientific as part number 7421.

2. Correction of ionization errors in EC
measurements

3. Correction of temperature errors in EC
measurements

4. Output processing

All example programs may require modification
by the user to fit the specific application's wiring
and programming needs. Example programs in
this manual assume that the orange lead is
connected to 1H, the white to 1L, the red to 2H,
the green to E2, and the black to E1.

2

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: P6 Full Bridge

01: 1 Rep
02: 15 2500 mV fast Range

(Use 5000 mV fast for 21X)
03: 1 IN Chan
04: 1 Excite all reps w/EXchan 1
05: 2500 mV Excitation

(5000 mV for 21X)
06: 1 Loc [:Rs ]
07: -.001 Mult
08: 1 Offset

02: P59 BR Transform Rf[X/(1-X)]

01: 1 Rep
02: 1 Loc [:Rs ]
03: 1 Multiplier (Rf)

Test the preliminary measurement against each
case and make a refined measurement.

03: P93 Case

01: 1 Case Loc Rs

04: P 83 If Case Location < F

01: 1.8 F
02: 30 Then Do

05: P5 AC Half Bridge

01: 1 Rep
02: 15 2500 mV fast Range

(Use 5000 mV fast for 21X)
03: 2 IN Chan
04: 1 Excite all reps w/EXchan 1
05: 2500 mV Excitation

(Use 5000 mV for 21X)
06: 1 Loc [:Rs ]
07: 1 Mult
08: 0 Offset

06: P95 End
07: P83 If Case Location < F

01: 9.25 F
02: 30 Then Do

08: P6 Full Bridge

01: 1 Rep
02: 15 2500 mV fast Range

(Use 5000 mV fast for 21X)
03: 1 IN Chan
04: 1 Excite all reps w/EXchan 1
05: 2500 mV Excitation

(5000 mV for 21X)
06: 1 Loc [:Rs ]
07: -.001 Mult
08: 1 Offset

09: P95 End
10: P83 If Case Location < F

01: 280 F
02: 30 Then Do

3

247 CONDUCTIVITY AND TEMPERATURE PROBES

11: P6 Full Bridge

01: 1 Rep
02: 14 250 mV fast Range

(Use 500 mV fast for 21X)
03: 1 IN Chan
04: 1 Excite all reps w/EXchan 1
05: 2500 mV Excitation

(Use 5000 mV for 21X)
06: 1 Loc [:Rs ]
07: -.001 Mult
08: 1 Offset

12: P95 End
13: P95 End
14: P59 BR Transform Rf[X/(1-X)]

01: 1 Rep
02: 1 Loc [:Rs ]
03: 1 Multiplier (Rf)

Subtract resistance errors (Rp) caused by the
blocking capacitors (0.005 kΩ) and the cable

-1

length (0.000032 kΩ ft

). Enter cable lead

length in nnn below.
15: P30 Z=F

01: nnn F Enter Lead Length

in Feet

02: 00 Exponent of 10
03: 5 Loc [:Rp ]

16: P37 Z=X*F

01: 5 Loc Rp
02: .00032 F
03: 5 Loc [:Rp ]

17: P37 Z=X*F

01: 5 Loc Rp
02: -.1 F
03: 5 Loc [:Rp ]

18: P34 Z=X+F

01: 5 Loc [Rp ]
02: -.005
03: 5 Loc [:Rp ]

NOTE: The cell constant (K

) is printed on the

c

label of each sensor. It is entered in place of
nnn in this segment.

20: P42 Z=1/X

01: 1 X Loc Rs
02: 2 Z Loc [:1/Rs ]

21: P37 Z=X*F

01: 2 X Loc 1/Rs
02: nnn F ENTER CELL

CONSTANT

03: 3 Z Loc [:Ct ]

Temperature Temperature is measured with a
single instruction, P11, that measures the
thermistor resistance and calculates
temperature. Output is °C when a multiplier of
1 and an offset of 0 is used. See Section 10 for
detailed information on the function of
Instruction P11.

22: P11 Temp 107 Probe

01: 1 Rep
02: 3 IN Chan
03: 2 Excite all reps w/EXchan 2
04: 4 Loc [:Temp °C ]
05: 1 Mult
06: 0 Offset

5.3 CORRECTION OF IONIZATION ERRORS IN
EC MEASUREMENT

Ionization caused by the excitation of the EC
sensor can cause large errors. Campbell
Scientific has developed a linear correction for
measurements between 0.005 and 0.44 mS cm
and a quadratic correction for measurements

-1

between 0.44 and 7.0 mS cm

. Corrections were
determined in standard salt solutions containing
KCl, Na

, NaHCO3, and NaCl.

2SO4

The following program segment automatically
chooses which correction to apply to the
measurement.

23: P89 If X<=>F

-1

,

19: P33 Z=X+Y

01: 1 X Loc Rs
02: 5 Y Loc Rp
03: 1 Z Loc [:Rs ]

EC is then calculated by multiplying the
reciprocal of resistance, which is conductance,
by the cell constant to arrive at EC.

4

01: 3 X Loc Ct
02: 4 <
03: .474 F
04: 30 Then Do

24: P37 Z=X*F

01: 3 X Loc Ct
02: .95031 F
03: 3 Z Loc [:Ct ]

247 CONDUCTIVITY AND TEMPERATURE PROBES

25: P34 Z=X+F

01: 3 X Loc Ct
02: -.00378 F

03: 3 Z Loc [:Ct ]
26: P94 Else
27: P55 Polynomial

01: 1 Rep

02: 3 X Loc Ct

03: 3 F(X) Loc [:Ct ]

04: -.02889 C0

05: .98614 C1

06: .02846 C2

07: 0.0000 C3

08: 0.0000 C4

09: 0.0000 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. A simple method of correcting
for this effect is to assume a linear relationship
between temperature and EC. This method
generally produces values to within 2% to 3% of
a measurement made at 25°C.

The best corrections are made when the
temperature coefficient is determined at a
temperature near field conditions. See Section
9 for details on how to determine the
temperature coefficient. If determining the
temperature coefficient is not possible, use a

-1

value of 2% °C

as a rough estimate.

The following program segment implements a
previously determined temperature coefficient
(TC) and calculates the corrected conductivity.

32: P34 Z=X+F

01: 9 X Loc TC PROCES
02: 100 F
03: 9 Z Loc [:TC PROCES]

33: P38 Z=X/F

01: 8 X Loc 100*Ct
02: 9 Y Loc TC PROCES
03: 10 Z Loc [:C25mScm-1]

5.5 OUTPUT PROCESSING

Over large ranges, EC is not linear and is best
reported as samples (70). In limited ranges,
averaging (71) measurements over time may be
acceptable. Convention requires that the
temperature at the time of the measurement be
reported.

6. CALIBRATION

6.1 CONVERSION FACTORS

1 S (Siemens) = 1 mho = 1/ohm
Although mS·cm

commonly used units of EC, the SI base unit is

-1

. The result of the example programs is

S·m
mS·cm

-1

EC measurements can be used to estimate
dissolved solids. For high accuracy, calibration
to the specific stream is required. However, for
rough estimates, values between 550 and 750

-1

/ mS·cm-1 are typical with the higher

mg·l
values generally being associated with waters
high in sulfate concentration (USGS Water­Supply Paper #1473, p. 99). A common
practice is to multiply the EC in mS·cm
to produce ppm or mg·l

6.2 TYPICAL RANGES

-1

and µS·cm-1 are the

-1

.

-1

by 500

29: P34 Z=X+F

01: 4 X Loc Temp °C

02: -25 F

03: 6 Z Loc [:A ]
30: P37 Z=X*F

01: 3 X Loc Ct

02: 100 F

03: 8 Z Loc [:100*Ct ]
31: P37 Z=X*F

01: 6 X Loc A

02: nnn F Enter TC (%°C

03: 9 Z Loc [:TC PROCES]

Single distilled water will have an EC of at least

-1

0.001 mS·cm
range from 0.002 to 0.042 mS·cm

. ECs of melted snow usually

-1

. ECs of

stream water usually range from 0.05 to 50.0

-1

mS·cm

, the higher value being close to the EC
of sea water (USGS Water-Supply Paper 1473,
p. 102).

6.3 FACTORY CALIBRATION

The 247 is shipped with a cell constant
calibrated in a 0.01 molal KCl solution at 25.0°C

-1

)

±0.05°C. The solution has a EC of 1.408 mS

-1

.

cm

5

247 CONDUCTIVITY AND TEMPERATURE PROBES

6.4 FIELD CALIBRATION

The cell constant is a dimensional number

-1

expressed in units of cm

. The unit cm-1 is

slightly easier to understand when expressed as

-2

cm·cm

. 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.

A field calibration of the 247 cell constant can
be accomplished as follows:

1. Make a 0.01 molal KCL solution by

dissolving 0.7456 g of reagent grade KCl in
1000 g of distilled water.

2. Clean the probe thoroughly with the black

nylon brush shipped with the 247 and a
small amount of soapy water. Rinse
thoroughly with distilled water, dry
thoroughly, and place in the KCl solution.

3. Connect the 247 to the datalogger using the

wiring described in Section 4. Enter the
following program into the datalogger.

The calibration solution temperature must be
between 1°C and 35°C; the polynomial in step 11
(58) corrects for temperature errors within this
range. The solution constant of 1.408 mS cm
entered in step 13 (37), is valid only for a 0.01
molal KCl solution. Location 8, generated by step
14, will contain the resultant cell constant.

01: P5 AC Half Bridge

01: 1 Rep
02: 15 2500 mV fast Range

(5000 mV fast for 21X)
03: 2 IN Chan
04: 1 Excite all reps w/EXchan 1
05: 2500 mV Excitation

(5000 mV for 21X)
06: 1 Loc [:Rs ]
07: 1 Mult
08: 0 Offset

02: P59 BR Transform Rf[X/(1-X)]

01: 1 Rep
02: 1 Loc [:Rs ]
03: 1 Multiplier (Rf)

03: P30 Z=F

01: nnn F Enter Lead Length

in Feet

02: 00 Exponent of 10
03: 5 Loc [:Rp ]

04: P37 Z=X*F

01: 5 Loc Rp
02: .00032 F
03: 5 Loc [:Rp ]

05: P37 Z=X*F

01: 5 Loc Rp
02: -.1 F
03: 5 Loc [:Rp ]

06: P34 Z=X+F

01: 5 Loc [Rp ]
02: -.005
03: 5 Loc [:Rp ]

07: P33 Z=X+Y

01: 1 X Loc Rs
02: 5 Y Loc Rp
03: 1 Z Loc [:Rs ]

08: P11 Temp 107 Probe

01: 1 Rep
02: 3 IN Chan
03: 2 Excite all reps w/EXchan 2
04: 2 Loc [:t]
05: 1 Mult
06: 0 Offset

09: P34 Z=X+F

01: 2 X Loc t
02: -25 F
03: 3 Z Loc [:(t-25).01]

-1

,

10: P37 Z=X*F

01: 3 X Loc (t-25).01
02: .01 F
03: 3 Z Loc [:(t-25).01]

11: P55 Polynomial

01: 1 Rep
02: 3 X Loc (t-25).01
03: 4 F(X) Loc [:f(t) ]
04: .99124 C0
05: -1.8817 C1
06: 3.4789 C2
07: -3.51 C3
08: -1.2 C4
09: -43 C5

12: P42 Z=1/X

01: 4 X Loc f(t)
02: 6 Z Loc [:1/f(t) ]

13: P37 Z=X*F

01: 6 X Loc 1/f(t)
02: 1.408 F
03: 7 Z Loc [:Act'l Con]

14: P36 Z=X*Y

01: 7 X Loc Act'l Con
02: 1 Y Loc Rs
03: 8 Z Loc [:Kc (cm-1)]

6

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
< 8.0%, 0.005 to 0.45 mS cm

-1

-1

Correction of Ionization Errors. Figures 8.1-1 and

8.1-2 show the amount of correction applied by the

example program to compensate for ionization
effects on the measurements. Also shown is an
ideal correction. Factors were derived by
measuring the standard solutions described in
Section 2.2 with values of 0.0234, 0.07, 0.4471,

-1

07, 1.413, 2.070, 3.920, and 7.0 mS cm

.

FIGURE 8.1-1. Plot of Ideal and Actual Correction between 0 and 0.44 mS cm

FIGURE 8.1-2. Plot of Ideal and Actual Correction between 0.44 and 7.0 mS cm

-1

-1

7

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. For the range of 0° to 50°C the
interchangeability error is predominantly offset and
can be determined with a single point calibration.
Compensation can then be done with an offset
entered in the measurement instruction. The bridge
resistors are 0.1% tolerance with a 10 ppm
temperature coefficient. Polynomial errors are
tabulated in Table 8.2-2 and plotted in Figure 8.2-1.

TABLE 8.2-1. Thermistor Interchangeability

Specification

Temperature

Temperature (°C) Tolerance (

−40 0.40

−30 0.40

−20 0.32

−10 0.25

0 to +50 0.20

TABLE 8.2-2. Polynomial Error

-40 to +56 <±1.0°C

-38 to +53 <±0.5°C

-24 to +48 <±0.1°C

±°C)

FIGURE 8.2-1. Error Produced by Polynomial Fit to Published Values

8

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 C
from Location 3. This number will be C
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.
This temperature will be t (in °C) in the
formula. Record C

at the new temperature

t

from Location 3. This number will be C in
the formula in Step 4.

4. Calculate the temperature coefficient (TC)

using the following formula.

)

25

= % / °C

25

TC = 100 *

(C - C

_____________

(t - 25) * C

Enter TC in the appropriate location (nnn)
as shown in the program segment in
Section 5.4.

10. INSTRUCTION 11 DETAILS

Understanding the details in this section are not
necessary for general operation of the 247
probe with CSI's dataloggers.

Instruction 11 outputs a precise 2 VAC
excitation (4 V with the 21X) and measures the
voltage drop due to the sensor resistance. The
thermistor resistance changes with
temperature. Instruction 11 calculates the ratio
of voltage measured to excitation voltage
(Vs/Vx) which is related to resistance, as shown
below:

Vs/Vx = 1000/(Rs+249000+1000)
where Rs is the resistance of the thermistor.
See the measurement section of the datalogger

manual for more information on bridge
measurements.

at 25°C

t

25

in

(Vs/Vx)*800. Resistance and datalogger output
at several temperatures are shown in Table 10-1.

TABLE 10-1. Temperature , Resistance, and

Datalogger Output

0.00 351017 -0.06

2.00 315288 1.96

4.00 283558 3.99

6.00 255337 6.02

8.00 230210 8.04

10.00 207807 10.06

12.00 187803 12.07

14.00 169924 14.06

16.00 153923 16.05

18.00 139588 18.02

20.00 126729 19.99

22.00 115179 21.97

24.00 104796 23.95

26.00 95449 25.94

28.00 87026 27.93

30.00 79428 29.95

32.00 72567 31.97

34.00 66365 33.99

36.00 60752 36.02

38.00 55668 38.05

40.00 51058 40.07

42.00 46873 42.07

44.00 43071 44.05

46.00 39613 46.00

48.00 36465 47.91

50.00 33598 49.77

52.00 30983 51.59

54.00 28595 53.35

56.00 26413 55.05

58.00 24419 56.70

60.00 22593 58.28

TABLE 10-2. Polynomial Coefficients

COEFFICIENT VALUE

C0 -53.4601
C1 9.08067
C2 -8.32569 x 10
C3 5.22829 x 10
C4 -1.67234 x 10
C5 2.21098 x 10

-01

-02

-03

-05

Instruction 11 then calculates temperature using a
fifth order polynomial equation correlating Vs/Vx
with temperature. The polynomial coefficients are
given in Table 10-2. The polynomial input is

9

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). Instruction 11's fast integration will
not reject 60 Hz noise.

Example 2. Sample CR10(X) Instructions

Using AC Half Bridge

01: P5 AC Half Bridge

01: 1 Rep
02: 22** 7.5 mV 60 Hz rejection Range
03: 9* IN Chan
04: 3* Excite all reps w/EXchan 3
05: 2000** mV Excitation
06: 11* Loc [:Air_Temp ]
07: 800 Mult
08: 0 Offset

02: P55 Polynomial

01: 1 Rep
02: 11* X Loc Air_Temp
03: 11* F(X) Loc [:Air_Temp ]
04: -53.46 C0
05: 90.807 C1
06: -83.257 C2
07: 52.283 C3
08: -16.723 C4
09: 2.211 C5

* Proper entries will vary with program and

datalogger channel and input location
assignments.

** On the 21X and CR7 use the 15 mV input

range and 4000 mV excitation.

12. LONG LEAD LENGTHS TEMPERATURE

If the 247-L/247W-L has lead lengths of more
than 300 feet, use the DC Half Bridge
instruction (Instruction 4) with a 2 millisecond
delay to measure temperature. The delay
provides a longer settling time before the
measurement is made. Do not use the
247-L/247W-L with long lead lengths in an
electrically noisy environment.

Example 3. Sample Program CR10 Using DC

Half Bridge with Delay

01: P4 Excite, Delay,Volt(SE)

01: 1 Rep
02: 2** 7.5 mV slow range
03: 9* IN Chan
04: 3* Excite all reps w/EXchan 3
05: 2 Delay (units .01sec)
06: 2000** mV Excitation
07: 11* Loc [:Temp_C ]
08: .4*** Mult
09: 0 Offset

02: P55 Polynomial

01: 1 Rep
02: 11* X Loc Temp_C
03: 11* F(X) Loc [:Temp_C ]
04: -53.46 C0
05: 90.807 C1
06: -83.257 C2
07: 52.283 C3
08: -16.723 C4
09: 2.211 C5

* Proper entries will vary with program and

datalogger channel and input location
assignments.

** On the 21X and CR7 use the 15 mV input

range and 4000 mV excitation.

*** Use a multiplier of 0.2 with a 21X and CR7.

10

13. 247 SCHEMATIC

247 CONDUCTIVITY AND TEMPERATURE PROBES

FIGURE 11-1. 247 Conductivity and Temperature Circuit Diagram

11

247 CONDUCTIVITY AND TEMPERATURE PROBES

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