Thermocouple Pod (Model EP306)• Plug and play installation with e-corder units• Use with either a K- or T-type thermocouple probe• –270 °C to 485 °C (K-type probe)• –270 °C to 385 °C (T-type probe)• Offset mode for relative measurements• Raw signal corresponds to NIST ITS-90
thermoelectric emf values for easy calibration

Description
A compact signal conditioner for use with an e-corder unit,
enabling continuous monitoring and recording of temperaturefrom K- or T-type thermocouple probes. It can be used in offset
mode to monitor small variations around a fixed temperature.
Please be familiar with the basic features of the Chart recording
software before attempting to use the Pod.

Thermocouple Compatibility
The Thermocouple Pod can be used with most K-type and T-type
thermocouples. Suitable thermocouple probes include:• ET405 K-type Thermocouple Probe• ET1400 T-type Thermocouple Probe

Applications
With a suitable probe the Pod can be used as a general
purpose laboratory thermometer for both research and teachinguse, including melting and boiling point determinations,
measurements of heats of reaction, and calorimetric kineticexperiments.

Theory of Operation
The Thermocouple Pod provides cold junction compensation
optimized for an ambient temperature of 20 °C and a primary
signal gain of 100. Secondary gain is provided by the e-corderunit, giving range settings shown in Table 1. A block diagram isshown in Figure 1.
The raw signal from the Pod corresponds to the thermoelectric
emf values for K- or T-type thermocouples as described by theNIST ITS-90 thermocouple database, available at:
http://srdata.nist.gov/its90/main/
An abridged set of emf/temperature values is shown in Table 2.
Bandwidth of the signal from the Pod is limited by a 30 Hz low
pass filter which maintains a fast response time for small probes.
Additional filter settings of 1, 2, 5, 10, and 20 Hz are provided
by the e-corder unit.

An ‘offset’ operating mode is provided so that small changes intemperature can be monitored accurately.

Operating Instructions
Connect the thermocouple probe to the connector on therear panel of the Thermocouple Pod. Connect the 8-pin DIN
connector cable from the Pod to an e-corder Pod port. Start theChart software and locate the Thermocouple Pod command in
the appropriate channel menu, which accesses the Thermocouple
Pod control window, Figure 2. Select an appropriate temperature
range and filter setting for your experiment. The signal will
be recorded in units of millivolts until calibrated by one of themethods outlined over the page.

Caution
Do not connect other devices such as eDAQ Amps or other
instruments to the corresponding BNC connector on the e-corderchannel used by the Pod.

Probe Error
Thermocouple probes are gauged against the ITS-90 tables ofthermoelectric emf values, Table 2.
Standard NIST K-type thermocouples can have an errorof 0.75% (above 0 °C), 2.0% (below 0 °C) or ±2.2 °C,
whichever is greater. ‘Special limits’ K-type thermocouples havean error of 0.4% or ±1.1 °C, whichever is greater.
Standard NIST T-type thermocouples can have an error of 0.75%(above 0 °C), 1.5% (below 0 °C) or ±1.0 °C, whichever isgreater. ‘Special limits’ T-type thermocouples can have an errorof 0.4% or ±0.5 °C, whichever is greater.
Also, some probes conform more closely to the NIST tables
and thus can have greater accuracy over specified temperature
ranges. For example, the ET1400 T-type thermocouple probe
has an error of less than ±0.1 °C between 0 – 50 °C.
If smaller errors are required it is necessary to calibrate the probewith accurately known temperature sources.

Ice Point
Reference
Thermocouple

+LPF
30 Hz

Temperature
OffsetPower
SupplyCable to e-corder

Device IDROMof interest. This method is largely superseded by the use of
the Thermocouple extension, above. If used with the ET1400
T-type Thermocouple Probe, and calibration values fromTable 1, an accuracy of ±0.1 °C can be expected over therange 0 – 50 °C.
For best results the Pod itself should be maintained at an
ambient temperature of 15 – 25 °C where the cold junction
compensation is optimized.

Calibration using Offset ModeFigure 1. Thermocouple Pod block diagram

Methods of Probe Calibration
For most applications, accuracy is limited by the probe rather
than the Pod itself. You can calibrate the probe for direct
temperature readings in one of four ways:• use the Chart Thermocouple extension which applies
a polynomial correction (down to –200 °C) according
to the ITS-90 thermoelectric emf tables for K- and T-type
thermocouples to provide a signal calibrated in units of °C, °F,
or K. This method is very convenient, resulting in a calibration
to the uncertainty limits (error) of the probe. If used with theET1400 T-type Thermocouple Probe, an accuracy of ±0.1 °C
can be expected over the range 0 – 50 °C. You can obtain
the extension by downloading it from http://www.edaq.com.
• use two accurately known temperature sources and theUnits Conversion feature of the Chart software. This results inaccurate calibration over small temperature ranges ( <10 °C ).
• use up to 12 known temperature sources, using theMultipoint Calibration extension of Chart software. This canresult in highly accurate calibration of the probe over an
extended temperature range, as long as accurately known
temperature sources are used. You can obtain the extension by
downloading it from http://www.edaq.com.
• use the Multipoint Calibration extension (download it fromhttp://www.edaq.com) to apply a series of known emf/
temperature calibration points, from Table 2, across the range

The Pod can be operated in offset mode to monitor small
temperature fluctuations accurately. First determine the probe
temperature as above. Then tick the Offset check box in theThermocouple control window, Figure 2, and use the offset knob
to zero the signal.
To calibrate the signal:• use the Units Conversion feature and enter 0 = 0 as thefirst calibration point. Then use the Seebeck coefficient at thattemperature, Table 2, to enter the second calibration point.
For example with a T-type probe, if the initial temperature is
25 °C, use 0.0406 mV = 1 °C (i.e., at 25 °C, a one degreechange in temperature will produce a 0.0406 mV change inthe signal)• use the Chart Thermocouple extension which will apply apolynomial correction based on the ITS-90 tables. This methodshould give adequate accuracy even over the larger ranges(10 and 25 °C) available in the offset mode.

Response time
The response time of the Pod is ultimately determined by its
maximum bandwidth of 30 Hz, which is greater than virtually allcommercially available thermocouple probes.
Larger probes will take longer to reach thermal equilibrium with
their surroundings. Small, exposed thermocouple junctions will
provide fastest response.

Tick this box to select Offset mode. The
knob on the front of the Pod can thenbe used to zero the signal, and therange menu displays settings of 1, 2,5, 12 and 25 °C for recording relative
temperature fluctuations.

Figure 2. Thermocouple Podcontrol window
Click this button to access theUnits Conversion dialog box.

Table 1. Thermocouple Pod temperature ranges.
Range setting(°C)

Actual range(mV)

Total gain

Actual range
K-type (°C)

Actual range
T-type (°C)

500±20x500

485

385

250±10x1000

246

213

125±5x2000

122

112

50±2x5000

50

50

25±1x10000

2525

12±0.5x20000

12.5

12.5

5±0.2x50000

55Specifications
Input impedance:

~1 kΩ

Gain:

x100

Table 2. Thermoelectric emf values† and Seebeckcoefficients* for K- and T-type thermocouples.
Temperature(°C)

K-typeemf(mV)

Seebeck
Coeficient(µV/°C)

T-typeemf
(mV)

–250
–200

Seebeck
Coeficient(µV/°C)–6.404

4.8–6.180

6.3–5.891

15.2–5.60315.7–150–4.91323.6–4.64822.3–100–3.55430.5–3.37928.4–50–1.88935.8–1.81933.9–10–0.39238.9–0.38337.8–5–0.19739.2–0.19338.300.000

39.5

0.000

38.8

50.198

39.7

0.195

39.1

100.397

39.9

0.391

39.4

150.597

40.1

0.589

39.9

200.798

40.3

0.790

40.3

25

1.000

40.5

0.992

40.6

Range settings:

5, 12, 25, 50, 125, 250, 500 °C(±0.2, 0.5, 1, 2, 5, 10, 20 mV)

30

1.203

40.7

1.196

41.1

Offset mode ranges:±1, 2, 5, 12, 25 °C(±0.05, 0.1, 0.2, 0.5, 1 mV)

35

1.407

40.9

1.403

41.6

Extent of offset:–50 °C to 385 °C (T-type), or 485 °C (K-type)

40

1.612

41.0

1.612

42.0

45

1.817

41.1

1.823

42.4

502.023

41.3

2.036

42.8

Output signal:±2 V maximum

Cold junction compensation:

Optimized at an ambient temperature of20 °C, 40.3 µV/°C

55

2.230

41.3

2.251

43.2

Accuracy:

0.1%60

2.436

41.4

2.468

43.6

DC drift:

2 µV/°C

65

2.644

41.5

2.687

44.1

70

2.851

41.5

2.909

44.5

Low pass filter settings:

1, 2, 5, 10, 20, 30 Hz

75

3.059

41.6

3.132

44.9

Response time (@ 30 Hz):~13 ms for 0 – 90% of final value.
Probe size will limit response time.

80

3.267

41.53.358

45.3

Amplifier noise:

1 µV p-p (0.1 to 10 Hz)

85

3.474

41.5

3.585

45.6

90

3.682

41.5

3.814

46.1

95

3.889

41.4

4.046

46.5

100

4.096

41.4

4.279

46.7

105

4.303

41.3

4.513

47.1

110

4.509

41.2

4.750

47.5

150

6.138

40.2

6.704

50.2

200

8.138

39.9

9.288

53.2

250

10.15340.7

12.01355.8

300

12.20941.5

14.86258.1

350

14.29341.9

17.81960.2

400

16.39742.2

20.87261.8

45018.516

42.5

–

–

500

20.64442.6––

Input connector:

Miniature thermocouple socket

Dimensions (l x w x h):

108 x 58 x 35 mm

Weight:~200 geDAQ Pty Ltd reserves the right to alter these specifications at any time.

Stacking and Unstacking Pods
Pods stack by clicking into place on
top of each other. To separate stacked
Pods, push the top Pod towards theback and then pull them apart fromthe back.

† Values from NIST ITS-90 data base at http://srdata.nist.gov/its90/main/* Seebeck coefficients determined for ±5 °C about the nominal temperature.

WARRANTY: eDAQ Hardware units are supported by a one year warranty

www.eDAQ.com
E-mail: info@edaq.com
e-corder is a registered trademark of eDAQ Pty Ltd.
All other trademarks are the property of their respective owners. PT7/03

Document Number: U-EP306-0104
Copyright © eDAQ 2004