Campbell 108 User Guide

Model 108 Temperature Probe

Revision: 6/10

Copyright © 1985-2010

Campbell Scientific, Inc.

Warranty and Assistance

The MODEL 108 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. 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 within their territories. Please visit
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#_____
815 West 1800 North
Logan, Utah 84321-1784

For all returns, the customer must fill out a “Declaration of Hazardous Material
and Decontamination” form and comply with the requirements specified in it.
The form is available from our website at
completed form must be either emailed to [e-mail]
435-750-9579. Campbell Scientific will not process any returns until we
receive this form. If the form is not received within three days of product
receipt or is incomplete, the product will be returned to the customer at the
customer’s expense. Campbell Scientific reserves the right to refuse service on
products that were exposed to contaminants that may cause health or safety
concerns for our employees.

www.campbellsci.com/repair

. A

or faxed to

108 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. General .........................................................................1

1.1 Specifications............................................................................................1

2. Accuracy.......................................................................2

3. Installation....................................................................3

3.1 Air Temperature........................................................................................3

3.1.1 Siting...............................................................................................3

3.1.2 Assembly and Mounting.................................................................4

3.2 Soil Temperature ......................................................................................5

3.3 Water Temperature...................................................................................5

4. Wiring............................................................................5

5. Programming ...............................................................6

5.1 CRBasic....................................................................................................6

5.2 Edlog.........................................................................................................7

5.3 Example Programs....................................................................................7

5.3.1 Example Program for CR1000 Datalogger.....................................7

5.3.2 Example Program for CR10X Datalogger......................................8

5.4 Electrical Noisy Environments.................................................................8

5.5 Long Lead Lengths...................................................................................9

6. Measurement Details.................................................10

6.1 Therm108 Instruction.............................................................................10

6.2 AC Half Bridge and Polynomial Instructions.........................................10

7. Maintenance and Calibration....................................12

8. Troubleshooting ........................................................13

Figures

2-1. 108 Probe Polynomial Error Curve.........................................................3

2-2. 108 Probe Schematic...............................................................................3

3-1. 108 and 41303-5A Radiation Shield on Tripod Mast .............................4

3-2. 108 and 41303-5A Radiation Shield on a CM200 Series Crossarm .......5

i

108 Table of Contents

Tables

1-1. Recommended Lead Lengths ................................................................. 1

2-1. Thermistor Interchangeability Specification........................................... 2

2-2. Polynomial Error .................................................................................... 2

4-1. Connections to Campbell Scientific Dataloggers................................... 6

5-1. Wiring for Example Programs................................................................ 7

6-1. Polynomial Coefficients ....................................................................... 11

6-2. Actual Temperature, Sensor Resistance, and Computed Temperature. 11

ii

Model 108 Temperature Probe

1. General

The 108 temperature probe uses a thermistor to measure temperature. The
probe is designed for measuring air/soil/water temperatures. For air
temperature, a 41303-5A radiation shield is used to mount the 108 Probe and
limit solar radiation loading. The 108 temperature probe is designed to be
buried or submerged in water up to 50 feet (21 psi).

For the –L option, the probe’s cable terminates in pigtails that connect to a
Campbell Scientific datalogger or a connector that attaches to a prewired
enclosure. For the –LC option, the probe’s cable is fitted with a connector that
attaches to an ET107, ET106, or MetData1 Weather Station. Throughout this
manual, 108 will refer to both the 108-L and 108-LC unless specified
otherwise.

Lead length for the 108-L and 108-LC is specified when the sensor is ordered.
Table 1-1 gives the recommended lead length for mounting the sensor on a
tripod or tower.

TABLE 1-1. Recommended Lead Lengths

2 m Height Atop a tripod or tower via a 2 ft crossarm such as the CM202

Mast/Leg CM202 CM6 CM10 CM110 CM115 CM120 UT10 UT20 UT30

9' 11' 11' 14' 14' 19' 24' 14' 24' 37'

Note: Add two feet to the cable length if you are mounting the enclosure on the leg base of a light-weight tripod.

The 108 ships with:

(1) Resource CD

1.1 Specifications

Sensor: BetaTherm 100K6A Thermistor

Temperature
Measurement Range: -5° to +95°C

Thermistor
Survival Range: -50° to +100°C

Thermistor
Interchangeability Error: Typically <±0.2°C over 0°C to 70°C ±0.3 @ 95°C.

Steinhart-Hart
Equation Error: ≤±0.01°C (CRBasic dataloggers only)

1

Model 108 Temperature Probe

Polynomial
Linearization Error: <±0.5°C over -5°C to +90°C (Edlog dataloggers
only)

Time Constant in Air: 200 ± 10 seconds

Maximum Lead Length: 1000 ft.

NOTE

2. Accuracy

The black outer jacket of the cable is Santoprene
compound was chosen for its resistance to temperature extremes,
moisture, and UV degradation. However, this jacket will
support combustion in air. It is rated as slow burning when
tested according to U.L. 94 H.B. and will pass FMVSS302.
Local fire codes may preclude its use inside buildings.

The overall probe accuracy is a combination of the thermistor's
interchangeability specification, the precision of the b ridge resistors, and the
Steinhart-Hart equation error (CRBasic dataloggers) or the polynomial error
(Edlog dataloggers). In a "worst case" all errors add to an accuracy of ±0.3°C
over the range of -3° to 90°C and ±0.7°C over the range of -5°C to 95°C. The
major error component is the interchangeability specification of the thermistor,
tabulated in Table 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 2-2 and plotted in Figure
2-1.

TABLE 2-1. Thermistor

Interchangeability Specification

®

rubber. This

2

Temperature (°C)

−5

0 to +50 0.20
+70 0.20
+90 0.31

TABLE 2-2. Polynomial Error

-5° to +95° <±0.5°C

-3° to +90° <±0.1°C

Temperature
Tolerance (±°C)

0.25

Model 108 Temperature Probe

FIGURE 2-1. 108 Probe Polynomial Error Curve

(Edlog dataloggers only)

3. Installation

3.1 Air Temperature

3.1.1 Siting

FIGURE 2-2. 108 Probe Schematic

For air temperature measurements, sensors should be located over an open
level area at least 9 m (EPA) in diameter. The surface should be covered by
short grass, or where grass does not grow, the natural earth surface. Sensors
should be located at a distance of at least four times the height of any nearby
obstruction, and at least 30 m (EPA) from large paved areas. Sensors should
be protected from thermal radiation, and adequately ventilated.

3

Model 108 Temperature Probe

3.1.2 Assembly and Mounting

Standard air temperature measurement heights:

1.5 m +/- 1.0 m (AASC)

1.25 – 2.0 m (WMO)

2.0 m (EPA)

2.0 m and 10.0 m temperature difference (EPA)

The probe is designed to be buried or submerged in water up to 50’ (21 psi).

Tools required for installing on a tripod or tower:

• 1/2” open end wrench

• small screw driver provided with datalogger

• small Phillips screw driver

• UV resistant cable ties

• small pair of diagonal-cutting pliers

The 108 must be housed inside a radiation shield when the sensor will be
exposed to solar radiation (i.e., air temperature measurements made in the
field). The 41303-5A Radiation shield has a U-bolt for attaching the shield to
tripod mast / tower leg (Figure 3-1), or CM200 series crossarm (Figure 3-2).
The radiation shield ships with the U-bolt configur ed for attaching the shield to
a vertical pipe. Move the U-bolt to the other set of holes to attach the shield to
a crossarm.

41303-5A

108

Tripod Mast
or Tower Leg

FIGURE 3-1. 108 and 41303-5A Radiation Shield on a Tripod Mast

4

Model 108 Temperature Probe

r

41303-5A

108

Tripod Mast o
Tower Leg

CM200 Series Crossarm

FIGURE 3-2. 108 and 41303-5A Radiation Shield on a

CM200 Series Crossarm

The 108 is held within the 41303-5A by a mounting clamp on the bottom plate
of the 41303-5A (Figure 3-2). Loosen the two mounting clamp screws, and
insert the sensor through the clamp and into the shield. Tighten the screws to
secure the sensor in the shield, and route the sensor cable to the instrument
enclosure. Secure the cable to the tripod/tower using cable ties.

3.2 Soil Temperature

3.3 Water Temperature

4. Wiring

The 108 is suitable for shallow burial only. It should be placed horizontally at
the desired depth to avoid thermal conduction from the surface to the
thermistor. Placement of the cable inside a rugged conduit may be advisable
for long cable runs, especially in locations subject to digging, mowing, traffic,
use of power tools, or lightning strikes.

The 108 can be submerged to 50 feet. Please note that the 108 is not weighted.
Therefore, the installer should either add a weighting system or secure the
probe to a fixed or submerged object.

The connection of a 108-L to a Campbell Scientific datalogger is given in
Table 4-1. Refer to the ET107, ET106, or MetData1 manual for connecting a
108-LC to the weather station. Temperature is measured with one Single­Ended input channel and a Voltage Excitation channel. Multiple probes can be
connected to the same excitation channel (the number of probes per excitation
channel is physically limited by the number of lead wires that can be inserted
into a single voltage excitation terminal, approximately six).

5

Model 108 Temperature Probe

TABLE 4-1. Connections to Campbell Scientific Dataloggers

5. Programming

NOTE

Color

Black Voltage

Description

Excitation

CR800
CR850
CR5000
CR3000
CR1000

Switched
Voltage

CR510
CR500
CR10(X)

Switched
Excitation

21X
CR7
CR23X

Switched
Excitation

Excitation

Red Temperature

Signal
Purple Signal Ground
Clear Shield

Single-Ended
Input

Single-Ended
Input

AG
G

Single-Ended
Input

This section is for users who write their own datalogger
programs. A datalogger program to measure this sensor can be
generated using Campbell Scientific’s Short Cut Program
Builder software. You do not need to read this section to use
Short Cut.

5.1 CRBasic

The datalogger is programmed using either CRBasic or Edlog. Dataloggers
that use CRBasic include our CR800, CR850, CR1000, CR3000, CR5000, and
CR9000(X); see Section 5.1. Dataloggers that use Edlog include our CR510,
CR10(X), CR23X, and CR7; see Section 5.2. CRBasic and Edlog are included
in our LoggerNet, PC400, and RTDAQ software.

If applicable, please read “Section 5.4—Electrically Noisy Environments” and
“Section 5.5—Long Lead Lengths” prior to programming your datalogger.
Measurement details are provided in Section 6.

The Therm108 measurement instruction is used with dataloggers that are
programmed with CRBasic to measure the 108 probe. Therm108 makes a half
bridge voltage measurement, and converts the measurement result to
temperature using the Steinhart-Hart equation. With a multiplier of 1 an d an
offset of 0, the output is temperature in degrees C. With a multiplier of 1.8 and
an offset of 32, the output is temperature in degrees F.

6

5.2 Edlog

The AC Half Bridge measurement instruction (P5), is used with dataloggers
that are programmed with Edlog to measure the 108 probe. Instruction P5
makes a half bridge measurement, and the measurement result is converted to
temperature by the Polynomial Instruction (P55).

5.3 Example Programs

TABLE 5-1. Wiring for Example Programs

Color Description CR1000 CR10X

Black Excitation EX1 or VX1 E1
Red Signal SE1 SE1
Purple Signal Ground
Clear Shield

Both example programs measure a 108 temperature probe every second and
store a 60 minute average temperature.

Model 108 Temperature Probe

AG
G

5.3.1 Example Program for CR1000 Datalogger

'CR1000
'This example program measures a single 108 Thermistor probe
'once a second and stores the average temperature every 60 minutes.

'Declare the variables for the temperature measurement

Public T108_C

'Define a data table for 60 minute averages:

DataTable(Table1,True,-1)
DataInterval(0,60,Min,0)
Average(1,T108_C,IEEE4,0)
EndTable

BeginProg
Scan(1,Sec,1,0)

'Measure the temperature

Therm108(T108_C,1,1,Vx1,0,_60Hz,1.0,0.0)

'Call Data Table

CallTable(Table1)
NextScan
EndProg

7

Model 108 Temperature Probe

5.3.2 Example Program for CR10X Datalogger

;{CR10X}

*Table 1 Program
01: 1.0000 Execution Interval (seconds)

1: AC Half Bridge (P5)
1: 1 Reps
2: 23 25 mV 60 Hz Rejection Range ; 50 mV range on the 21X and CR7
3: 1 SE Channel
4: 1 Excite all reps w/Exchan 1
5: 1000 mV Excitation ; 2000 mV on the 21X and CR7
6: 1 Loc [ T108_C___ ]
7: 200 Multiplier
8: 0 Offset

2: Polynomial (P55)
1: 1 Reps
2: 1 X Loc [ T108_C___ ]
3: 1 F(X) Loc [ T108_C___ ]
4: -26.97 C0
5: 69.635 C1
6: -40.66 C2
7: 16.573 C3
8: -3.455 C4
9: 0.301 C5

3: If time is (P92)
1: 0 Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 10 Set Output Flag High (Flag 0)

4: Set Active Storage Area (P80)
1: 1 Final Storage Area 1
2: 101 Array ID

5: Real Time (P77)
1: 1220 Year,Day,Hour/Minute (midnight = 2400)

6: Average (P71)
1: 1 Reps
2: 1 Loc [ T108_C___ ]

8

5.4 Electrical Noisy Environments

AC power lines, pumps, and motors, can be the source of electrical noise. If
the 108 probe or datalogger is located in an electrically noisy environment, the
108 probe should be measured with the 60 or 50 Hz rejection option as shown
in Examples 5.4-1 and 5.4-2.

Example 5.4-1. CR1000 Measurement Instruction with 60 Hz Noise
Rejection

Therm108(T108_C,1,1,1,0,_60Hz,1.0,0.0)

Example 5.4-2. CR10X Example with 60 Hz Noise Rejection

1: AC Half Bridge (P5)
1: 1 Reps
2: 23 25 mV 60 Hz Rejection Range
3: 1 SE Channel
4: 1 Excite all reps w/Exchan 1
5: 1000 mV Excitation
6: 1 Loc [ T108_C___ ]
7: 200 Multiplier
8: 0 Offset

5.5 Long Lead Lengths

If the 108 has lead lengths of more than 300 feet, use the DC Half Bridge
instruction (Instruction 4) with a 20 millisecond delay to measure temperature.
The delay provides a longer settling time before the measurement is made. For
CRBasic loggers, the 60 and 50 Hz integration options include a 3 ms settling
time; longer settling times can be entered into the Settling Time parameter. Do
not use the 108 with long lead lengths in an electrically noisy environment.

Model 108 Temperature Probe

Example 5.5-1. CR1000 Measurement Instruction with 20 mSec (20000
uSec) Delay

Therm108(T108_C,1,1,1,20000,_60Hz,1.0,0.0)

Example 5.5-2. CR10X Measurement Instructions

01: Excite, Delay,Volt(SE) (P4)
1: 1 Rep
2: 3** ±25 mV slow range
3: 9* IN Chan
4: 3* Excite all reps w/EXchan 3
5: 2 Delay (units .01sec)
6: 1000** mV Excitation
7: 11* Loc [:Temp_C ]
8: .2*** Mult
9: 0 Offset

02: Polynomial (P55)
1: 1 Reps
2: 11 X Loc [ Tmp108C ]
3: 11 F(X) Loc [ Tmp108C ]
4: -26.97 C0
5: 69.635 C1

9

Model 108 Temperature Probe

6: -40.66 C2
7: 16.573 C3
8: -3.455 C4
9: .301 C5

* Proper entries will vary with program and datalogger channel and input location assignments.
** On the 21X and CR7 use the 50 mV input range and 2000 mV excitation.
*** Use a multiplier of 0.1 with a 21X and CR7.

6. Measurement Details

Understanding the details in this section is not necessary for general operation
of the 108 probe with CSI’s dataloggers.

6.1 Therm108 Instruction

Therm108 instruction applies a precise 2500 mV excitation voltage and
measures the voltage drop across the 1K ohm resistor. The ratio of measured
voltage (Vs) to the excitation voltage (Vx) is related to thermistor resistance
(Rs), and the 1000 and 40K ohm fixed resistors as shown below:

Vs/Vx = 1000/(Rs+40000+1000)

Therm108 calculates Rs from the voltage ratio, and converts Rs to temperature
using the Steinhart-Hart equation:

3

T = 1/(A+B(LnRs)+C(LnRs)

Where T is the temperature returned in degrees Celsius, and A, B, and C are
coefficients provided by the thermistor manufacturer:

A = 8.271111E-4
B = 2.088020E-4
C = 8.059200E-8

) – 273.15

6.2 AC Half Bridge and Polynomial Instructions

The AC Half Bridge (P5) instruction applies a precise AC excitation voltage
and measures the voltage drop across the 1K ohm resistor. The ratio of
measured voltage (Vs) to the excitation voltage (Vx) is related to thermistor
resistance (Rs), and the 1000 and 40K ohm fixed resistors as shown below:

Vs/Vx = 1000/(Rs+40000+1000)

The Polynomial (P55) instruction converts the measurement result Vs/Vx *
200 to temperature using a 5
are shown in Table 6-1. Thermistor resistance, and computed temperature over
a -10 to +84 degree Celsius range is shown in Table 6-2.

th

order polynomial. The polynomial coefficients

10

TABLE 6-1. Polynomial

Coefficients

Coefficient Value

C0 -26.97
C1 69.635
C2 -40.66
C3 16.573
C4 -3.455
C5 0.301

TABLE 6-2. Actual Temperature, Sensor

Resistance, and Computed Temperature

Model 108 Temperature Probe

Temperature
°C

Resistance
OHMS

Output
°C

-10.00 612366 -9.02

-8.00 546376 -7.36

-6.00 488178 -5.63

-4.00 436773 -3.83

-2.00 391294 -1.97

0.00 351017 -0.05

2.00 315288 1.91

4.00 283558 3.91

6.00 255337 5.93

8.00 230210 7.96

10.00 207807 10.00

12.00 187803 12.04

14.00 169924 14.07

16.00 153923 16.09

18.00 139588 18.10

20.00 126729 20.09

22.00 115179 22.07

24.00 104796 24.05

26.00 95449 26.02

28.00 87026 27.99

30.00 79428 29.97

32.00 72567 31.94

34.00 66365 33.93

36.00 60752 35.93

38.00 55668 37.93

40.00 51058 39.94

42.00 46873 41.96

44.00 43071 43.98

46.00 39613 46.00

48.00 36465 48.02

50.00 33598 50.03

52.00 30983 52.03

11

Model 108 Temperature Probe

54.00 28595 54.03

56.00 26413 56.03

58.00 24419 58.02

60.00 22593 60.01

62.00 20921 61.99

64.00 19388 63.98

66.00 17981 65.97

68.00 16689 67.96

70.00 15502 69.96

72.00 14410 71.97

74.00 13405 73.98

76.00 12479 75.99

78.00 11625 78.01

80.00 10837 80.02

82.00 10110 82.03

84.00 9438.1 84.04

86.00 8816.9 86.03

88.00 8241.9 88.00

90.00 7709.7 89.96

92.00 7216.3 91.89

94.00 6758.9 93.80

96.00 6334.5 95.67

98.00 5940.5 97.51

100.00 5574.3 99.31

7. Maintenance and Calibration

The 108 Probe requires minimal maintenance. Check monthly to make sure
the radiation shield is clean and free from debris. Periodically check cabling
for signs of damage and proper moisture intrusion.

For most applications it is unnecessary to calibrate the 108 to eliminate the
thermistor offset. However, for those users that are interested, the following
briefly describes calibrating the 108 probes.

A single point calibration can be performed to determine the 108 temperature
offset (thermistor interchangeability). For Edlog dataloggers, the value of the
offset must be chosen so that the probe outputs the temperature calculated by the
polynomial, not the actual calibration temperature. For example, a 108 is placed
in a calibration chamber that is at 0°C and the probe outputs 0.1°C. An offset of

-0.15 is required for Edlog dataloggers, because at 0°C the polynomial calculates
a temperature of -0.05°C.

NOTE

For all factory repairs and recalibrations, customers must get a
returned material authorization (RMA). Customers must also
properly fill out a “Declaration of Hazardous Material and
Decontamination” form and comply with the requirements
specified in it. Refer to the “Warranty and Assistance” page for
more information.

12

8. Troubleshooting

Symptom: Temperature is NAN, -INF, -9999, -273

Verify the red wire is connected to the correct Single-Ended analog input
channel as specified by the measurement instruction, and the purple wire is
connected to datalogger ground.

Symptom: Temperature is NAN, -26

Verify the black wire is connected to the switched excitation channel as
specified by the measurement instruction.

Symptom: Incorrect Temperature

Verify the multiplier and offset parameters are correct for the desired units
(Section 5). Check the cable for signs of damage and possible moisture
intrusion.

Symptom: Unstable Temperature

Try using the 60 or 50 Hz integration op tions, or increasing the settling time as
described in Sections 5.4 and 5.5. Make sure the clear shield wire is connected
to datalogger ground, and the datalogger is properly grounded.

Model 108 Temperature Probe

13

Model 108 Temperature Probe

14

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