Omega TC-08 User Manual 2

User’sGuide

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TC-08

8 Channel Thermocouple

USB Data Acquisition Module

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				Contents	I
Contents
1 Introduction.....................................................................................................................................					1
1		Overview...........................................................................................................................................			1
2		Installing...........................................................................................................................................the driver			1
3		Connecting...........................................................................................................................................the USB TC-08			1
4		Safety...........................................................................................................................................warning			4
2 Product information.....................................................................................................................................					5
1		Specifications...........................................................................................................................................			5
	2 How a thermocouple works...........................................................................................................................................				6
3 Technical reference.....................................................................................................................................					7
1		Introduction...........................................................................................................................................			7
2		Modes...........................................................................................................................................of operation			7
		1	Introduction...........................................................................................................................................		7
		2 Streaming...........................................................................................................................................mode			8
		3	Get Single...........................................................................................................................................mode		10
		4 Legacy ...........................................................................................................................................mode			12
3		Driver...........................................................................................................................................routines			14
		1	Introduction...........................................................................................................................................		14
		2 New USB...........................................................................................................................................mode and legacy mode			15
		3 New USB...........................................................................................................................................mode only			29
		4	Legacy ...........................................................................................................................................mode only		34
	4 Programming...........................................................................................................................................				41
		1	Introduction...........................................................................................................................................		41
		2 C and C++...........................................................................................................................................			41
		3	Delphi ...........................................................................................................................................		41
		4	Excel ...........................................................................................................................................		42
		5 LabVIEW...........................................................................................................................................			42
		6	Visual Basic...........................................................................................................................................		42
		7	Agilent...........................................................................................................................................VEE		42
5		Troubleshooting...........................................................................................................................................			43
6		Glossary...........................................................................................................................................			44
Index..............................................................................................................................................					47

Introduction 1

1 Introduction

1.1Overview

The USB TC-08 is a temperature and voltage logger designed to support multiple thermocouples. With the accompanying TC-08 software, the unit can be used with any laptop or PC running Windows XP SP2 or Vista. If you are technically-minded and want to tailor the product to a particular application, you can write your own programs with the supplied driver.

The driver provides cold junction compensation for thermocouples. The TC-08 software supports up to 20 USB TC-08 devices and the driver can support more (as many as 64, if you have a high-specification PC).

This manual describes the physical and electrical properties of the USB TC-08, and provides an explanation of how to use the software drivers. For information on the USB TC-08 software, please consult the software help file.

1.2Installing the driver

The driver is installed automatically when you install the TC-08 software. Alternatively, you can download the driver from our website at http://www.omega.com.

1.3Connecting the USB TC-08

Please note: do not connect the USB TC-08 until you have installed the

software and restarted your PC.

To begin using the USB TC-08, connect it to the USB port on your computer using the cable provided. Next, connect a thermocouple to one of the thermocouple input connectors. To complete the installation, select the USB TC-08 unit and thermocouple type in the TC-08 software as follows:

1.Start up the TC-08 Recorder

2.Select New Settings from the File menu.

The Recording dialog box appears:

3. Click the OK button.

The Sampling Rate dialog box appears

2 TC-08 User's Guide

4.Click the OK button.

The Converter details dialog box appears

5.Select USB TC-08 from the drop-down list of converters.

The device name and serial number should appear in the USB Devices pane and the USB enumeration progress bar gradually expand to 100%. If the progress bar does not start moving, disconnect and reconnect the USB TC-08, then click

Refresh.

6.In the USB Devices pane, select the USB TC-08. If you are using more than one USB TC-08, check the serial number on the bottom of the device so that you know which one to select from the list

7.Click the OK button.

The following dialog box appears

Introduction 3

8.In the TC-08 Channels window, double-click on Channel 1 unused.

The Edit TC-08 Channel dialog box appears

9.From the Thermocouple drop-down list, select the type of thermocouple you are using and click OK.

The TC-08 Channels dialog box reappears.

10.Click OK.

Channel 1 should now appear in the monitor window with the current temperature

reading.

4TC-08 User's Guide

1.4Safety warning

We strongly recommend that you read the general safety information below before using your product for the first time. If the equipment is not used in the manner specified, then the protection provided may be impaired. This could result in damage to your computer and/or injury to yourself or others.

Maximum input range

The USB TC-08 is designed to measure voltages in the range of ±70 mV. Any voltages in excess of ±30 V may cause permanent damage to the unit.

Mains voltages

These products are not designed for use with mains voltages.

Safety grounding

The ground of every product is connected directly to the ground of your computer through the interconnecting cable provided. This is done in order to minimise interference. If the PC (especially laptop) is not grounded, reading stability cannot be guaranteed and it may be necessary to manually ground the equipment.

Take care to avoid connecting the inputs of the product to anything which may be at a hazardous voltage. If in doubt, use a meter to check that there is no hazardous AC or DC voltage. Failure to check may cause damage to the product and/or computer and could cause injury to yourself or others.

Take great care when measuring temperatures near mains equipment. If a sensor is accidentally connected to mains voltages, you risk damage to the converter or your computer and your computer chassis may become live.

You should assume that the product does not have a protective safety earth. Incorrect configuration or use of the device to measure voltages outside the maximum input range can be hazardous.

Repairs

The unit contains no user-serviceable parts: repair or calibration of the unit requires specialised test equipment and must be performed by Omega Engineering.

Product information	5

2	Product information
2.1	Specifications
	Resolution	20 bits (16.25 NFR)
	Thermocouple types	B,E,J,K,N,R,S,T
	Number of input channels	8
	Conversion time - per active channel	100 ms
	Conversion time - CJC	100 ms
	Uncalibrated accuracy	The sum of ±0.2% and ±0.5°C
	Full scale input	±70 mV
	Common mode range	±7.5 V
	Overvoltage protection	±30 V
	Input impedance	2 MΩ
	Input connectors	8 x miniature thermocouple
	Output connector	USB upstream connector
	Power requirements	No power supply required
	Environmental conditions	0 to 50°C, 25% to 75% humidity
		Quoted accuracy over 20 - 30°C
		NOT water-resistant

Note: The resolution and accuracy depend upon the thermocouple type and the temperature range. Below is a list of the thermocouples and temperature ranges supported by the USB TC-08.

	Actual measurable range	Theoretical ranges
CJC	-5°C to 70°C	N/A
Type B	20°C to 1820°C (CJC must be	0°C to 1820°C
	>20°C)
Type E	-270°C to 910°C	-270°C to 1000°C
Type J	-210°C to 1200°C	-210°C to 1200°C
Type K	-270°C to 1370°C	-270°C to 1370°C
Type N	-270°C to 1300°C	-270°C to 1300°C
Type R	-50°C to 1760°C	-50°C to 1760°C
Type S	-50°C to 1760°C	-50°C to 1760°C
Type T	-270°C to 400°C	-270°C to 400°C

6TC-08 User's Guide

2.2How a thermocouple works

In a closed circuit of two dissimilar metals (a thermocouple), an electric current flows when one of the two junctions is heated with respect to the other. The current continues to flow as long as the two junctions are at different temperatures. The magnitude and direction of the current is a function of the temperature difference between the junctions and of the thermal properties of the metals used in the circuit. This phenomenon is known as the Seebeck Effect.

The conductors can be made of any two dissimilar metals, and when the hot junction is heated the current flow can be observed. If the positions of the hot and cold junctions are reversed, current flows in the opposite direction.

A thermocouple circuit actually generates a measurable, low-voltage output that is almost directly proportional to the temperature difference between the hot junction and the cold junction. A change in this temperature difference produces some net change in the voltage.

Note: More information on choosing and using thermocouples can be found at www.omega.com.

Technical reference	7

3	Technical reference

3.1Introduction

The USB TC-08 is supplied with driver routines that you can build into your own programs. The USB TC-08 driver supports Windows XP SP2 and Windows Vista.

Once you have installed the software, the Examples directory will contain the drivers and a selection of examples of how to use the drivers.

The driver is supplied as a Windows DLL. The DLL uses the C stdcall calling convention and can be used with C, Delphi and Visual Basic programs. It can also be used with programs like Microsoft Excel, where the macro language is a form of Visual Basic.

3.2Modes of operation

3.2.1Introduction

The USB TC-08 is designed for three specific modes of operation to suit a variety of applications. The following modes are supported:

Streaming mode

Get Single mode

Legacy mode

8TC-08 User's Guide

3.2.2Streaming mode

Streaming mode is an operational mode in which the USB TC-08 unit samples data and returns it to the computer in an unbroken sequence, using the onboard clock to ensure accurate timing.

The unit can buffer up to two sets of readings at once. To avoid loss of readings, make sure that another application on the PC - including the one you are writing - does not prevent the driver from collecting readings for more than three sampling intervals.

To allow the driver to sample continuously, call the Windows Sleep() function in any sampling loops (see example below) to make sure that your application does not use too much processor time.

Hint: Try not to use a Sleep() call for less than 50-100 milliseconds, e.g.,

Sleep(50) or Sleep(100). If you are programming a Windows GUI application, a good alternative to sampling loops is the WM_TIMER message.

Technical reference	9

Example

The following code is a fragment of a C application demonstrating how to use

Streaming mode with the USB TC-08 driver:

//==================================================

// Setting up and running the unit in Streaming mode

//==================================================

usb_tc08_set_mains(handle, 0); // use 50Hz mains noise rejection

for (channel = 0; channel < 9; channel++)

{

//set each channel up as a type K thermocouple

//channel 0 is the cold junction and will be enabled

//by setting the third argument to anything other than ' ' usb_tc08_set_channel(handle, channel, 'K');

}

//find out how fast the unit can sample in its current setup state minimum_interval = usb_tc08_get_minimum_interval_ms(handle);

usb_tc08_run(handle, minimum_interval); // sample as fast as possible

//not required (just illustrates that the application

//can be idle while the driver collects the readings) Sleep(10000);

//use a two dimensional array with an array of readings for each channel

//In a real application, this would be a nested loop to regularly poll

//the unit for readings

for (channel = 0; channel < 9; channel++)

{

no_of_readings = usb_tc08_get_temp( handle, &reading_buffer[channel], &times_buffer[channel], buffer_length, &overflows[channel], channel,

0, // degrees Celsius units

0); // do not fill missing readings

}

//finished polling, now do something with the readings

//if overflows[channel] is high, then one of the readings

//in reading_buffer[channel] has exceeded the input range

//of the USB TC-08

//only stop the unit when we've completely finished streaming usb_tc08_stop(handle);

Note: You should close down all other applications while you are performing any timing-critical data logging tasks. Check that the Windows scheduler does not have any activities planned during the logging session.

10TC-08 User's Guide

3.2.3Get Single mode

Get Single mode is an operational mode in which readings are produced on demand, using the usb_tc08_get_single function. Since the function relies entirely on the timing of the calling application, it is ideal for time intervals greater than 1 minute. If high-speed sampling is required, use Streaming mode.

Note: The function call overhead can be significant, since it takes approximately 360 ms to convert all 9 channels, equating to 40 ms per channel. To reduce this overhead, disable channels that are not required.

Technical reference	11

Example

The following code is a fragment of a C application demonstrating how to use Get

Single mode with the USB TC-08 driver:

//========================================================

// Setting up and converting readings with Get Single mode

//========================================================

usb_tc08_set_mains (handle, 0); // use 50Hz mains noise rejection

for (channel = 0; channel < 9; channel++)

{

//set each channel up as a type K thermocouple

//channel 0 is the cold junction and will be enabled

//by setting the third argument to anything other than ' ' usb_tc08_set_channel (handle, channel, 'K');

}

//find out the approximate conversion time

//for a call to usb_tc08_get_single

minimum_interval = usb_tc08_get_minimum_interval_ms (handle); printf("Conversion time: %d\n", minimum_interval);

// Collect 10 readings over approximately 9 minutes last_time = GetTickCount();

for (i = 0, i < 10, i++)

{

// do the conversion for all channels usb_tc08_get_single( handle,

value_array, // short value_array[9] &overflow_flags,

0);	// degrees Celsius units

// print out the values printf("\n\nTime: %d minute(s)", i); for (c = 0; c < 9; c++)

{

//check for overflows on each channel

//with a bitwise & comparator

//shift the comparison bit to match the channel if (overflow_flags & (1 << c))

{

printf("\nChannel %d overflowed", c);

}

else // no overflow

{

printf("\nChannel %d: %f", c, value_array[c]);

}

}

if (i < 9)

{

while (60000 > (GetTickCount() - last_time)) // 60000ms = 1 minute

{

Sleep(100); // let other applications run

}

last_time = GetTickCount();

}

}

12TC-08 User's Guide

3.2.4Legacy mode

Legacy mode is designed to aid developers who have already written code for the serial version of the TC-08 and are not yet ready to rewrite their code for the Streaming or Get Single modes available with the USB version. The legacy support is going to be phased out and will eventually be removed from the driver altogether. If you want full support in the future, use the Streaming or Get Single modes.

To allow code to be easily developed for both the serial version and the USB version of the TC-08, all the function names have been changed. The usb_tc08_legacy_set_channel function no longer supports offset and gain - this is now stored only as calibration information in the unit itself. The legacy routines will be familiar if you previously used the serial TC-08, but the following changes should be made to convert legacy applications:

Reference the new Header file

Reference the new Library file

Place the new DLL in the directory of the application

Set the mains frequency

Run and stop the unit

Store a handle returned from usb_tc08_open_unit instead of using the serial port number

Technical reference	13

Example

The following code is a fragment of a C application demonstrating how to use legacy

mode with the USB TC-08 driver:

//==========================================================

//Setting up and running the unit in Legacy mode

//This is designed to make it easier to adapt code written

//for the Serial TC08 for use with the USB TC08 //==========================================================

usb_tc08_set_mains(handle, 0); // use 50Hz mains noise rejection

for (channel = 1; channel < 9; channel++)

{

//set each channel up as a type K thermocouple

//switch off filtering for all channels

usb_tc08_legacy_set_channel(handle, channel, 'K', 0);

}

usb_tc08_legacy_run(handle);

last_cycle_no = 0; no_of_readings = 0;

while (no_of_readings < 50) // collect 50 readings

{

usb_tc08_legacy_get_cycle(handle, &this_cycle_no);

if (last_cycle_no != this_cycle_no)

{

last_cycle_no = this_cycle_no; no_of_readings++;

for (channel = 1; channel < 9; channel++)

{

usb_tc08_legacy_get_temp( &reading[channel], handle,

channel,

0);

}

//now do something with the readings

//check that they have not overflowed

//by comparing each reading with 2147483647L

//or LONG_MAX (include limits.h)

usb_tc08_legacy_get_cold_junction(handle, &cold_junction); // now do something with the cold junction temperature

}

}

usb_tc08_stop(handle);