F3–08THM–n 8-Channel Thermocouple Input

F3–08THM–n 8-Channel Thermocouple Input

F3–08THM–n

8-Channel

Thermocouple Input

In This Chapter. . . .

Ċ Introduction

Ċ Module Specifications

Ċ Setting the Module Switches

Ċ Connecting the Field Wiring

Ċ Module Operation

Ċ Writing the Control Program

1

9

9–2

F3–08THM–n 8-Channel Thermocouple Input

Introduction

Automatic

Conversion

The F3–08THM–n Thermocouple Input Module provides eight, differential thermocouple input channels (12-bit resolution). The module automatically converts type E, J, K, R, S or T thermocouple signals into direct temperature readings. No extra scaling or complex conversion is required. You can select between

_

F or

_

C operation.

This module is also available in versions specially designed to convert millivolt signal levels into direct digital values (0–4095). Two versions are available, one for

0–50mV and one for 0–100mV.

Hardware Features

The F3–08THM–n also features automatic cold junction compensation, thermocouple linearization, plus analog and digital filtering. The temperature calculation and linerazation are based on data provided by the National Bureau of

Standards.

Diagnostic

Features

Thermocouple burnout and other errors are automatically reported to the CPU. For example, if the thermocouple becomes disconnected, then a value of 4095 is assigned to that channel.

9–3

F3–08THM–n 8-Channel Thermocouple Input

Module Specifications

Analog Input

Configuration

Requirements

The following table provides the specifications for the F3–08THM–n Thermocouple

Input Module from FACTS Engineering. Review these specifications to make sure the module meets your application requirements.

Number of Channels

Input Ranges

Resolution

Input Impedance

Absolute Maximum Ratings

Cold Junction Compensation

Conversion Time

8, differential inputs

Type E: –270/1000

_

C, –450/1832

_

F

Type J: –210/760

_

C, –350/1390

_

F

Type K: –270/1370

_

C, –450/2500

_

F

Type R: 0/1768

_

C, –32/3214

_

F

Type S: 0/1768

_

C, –32/3214

_

F

Type T: –270/400

_

C, –450/752

_

F

–1: 0 – 50 mV

–2: 0–100 mV

12 bit (1 in 4096)

27K W DC

Fault protected input, 130 Vrms or 100 VDC

Automatic

15ms per channel, minimum

1 channel per CPU scan

Successive Approximation, 574

"

1 count (0.03% of full scale) maximum

0.35% of full scale

Converter Type

Linearity Error

Maximum Inaccuracy at 77

°

F

(25

°

C)

Accuracy vs. Temperature

Power Budget Requirement

External Power Supply

Operating Temperature

Storage Temperature

Relative Humidity

Environmental air

Vibration

Shock

Noise Immunity

57 ppm /

_

C maximum full scale

50 mA @ 9 VDC, 34 mA @ 24 VDC

None required

32

°

to 140

°

F (0

°

to 60

°

C)

–4

°

to 158

°

F (–20

°

to 70

°

C)

5 to 95% (non-condensing)

No corrosive gases permitted

MIL STD 810C 514.2

MIL STD 810C 516.2

NEMA ICS3–304

The F3–08THM–n Thermocouple Input appears as a 16-point module. The module can be installed in any slot configured for 16 points. See the DL305 User Manual for details on using 16 point modules in DL305 systems. The limitation on the number of analog modules are:

S

For local and expansion systems, the available power budget and

16-point module usage are the limiting factors.

9–4

F3–08THM–n 8-Channel Thermocouple Input

Setting the Module Jumpers

Jumper Locations

The module is set at the factory for

_

C thermocouple readings. If this is acceptable you do not have to change any of the jumpers. The following diagram shows how the jumpers are set.

Selecting

_

F or

_

C

Operation

WARNING: DO NOT change the calibration jumper settings. If you think this jumper has been changed, make sure it is NOT in the CAL position. All calibration is performed at the factory. Any changes to this may affect the module accuracy which could result in the risk of personal injury and/or equipment damage.

There is a jumper located on the bottom of the board that selects between

_

C and

_

F temperature measurements. This jumper (labeled

_

F) should be removed if you require

_

C measurements.

Measurement

Selection

_F CNTS

Selecting 0–4095

Operation

There is a jumper located on the bottom of the board that allows you to disable the direct temperature conversion feature. If you install a jumper on the CNTS pin, the temperature will be represented by a digital value between 0 and 4095. For example, an E type thermocouple would have a value of 0 for –450

_

F and a value of 4095 for 1832

_

F.

NOTE: If you are using the –1 (50mV) or the –2 (100mV) millivolt input versions, you should make sure this jumper is installed.

Remove this jumper for

_

C operation.

Measurement

Selection

_F CNTS

Install this jumper to obtain digital values (0 – 4095).

9–5

F3–08THM–n 8-Channel Thermocouple Input

Connecting the Field Wiring

Wiring Guidelines

Your company may have guidelines for wiring and cable installation. If so, you should check those before you begin the installation. Here are some general things to consider.

S

Use the shortest wiring route whenever possible.

S

Use shielded wiring and ground the shield at the signal source. Do not ground the shield at both the module and the source.

S

Don’t run the signal wiring next to large motors, high current switches, or transformers. This may cause noise problems.

S

Route the wiring through an approved cable housing to minimize the risk of accidental damage. Check local and national codes to choose the correct method for your application.

User Power Supply

Requirements

The F3–08THM–n receives all power from the base. A separate power supply is not required.

Wiring Diagram

Note 1: Terminate shields at the respective signal source

Note 2: Leave unused channels open (no connection)

Internal Module Wiring

THERMOCOUPLE

F3–08THM

A/D

CH1

See note

Examples of differential

Thermocouple wiring

CH3

CH6

CH8

Examples of grounded

Thermocouple wiring

+5

C

–6

+6

C

–4

+4

–5

–7

+7

–8

+8

C

+2

–3

+3

C

–1

+1

–2

Analog

Switch

C

–6

+6

–7

–4

+4

–5

+5

+7

–8

+8

C

+2

–3

+3

C

C

–1

+1

–2

9–6

F3–08THM–n 8-Channel Thermocouple Input

Module Operation

Channel Scanning

Sequence

Before you begin writing the control program, it is important to take a few minutes to understand how the module processes and represents the analog signals.

The F3–08THM–n module supplies1 channel of data per each CPU scan. Since there are eight channels, it can take up to eight scans to get data for all channels.

Once all channels have been scanned the process starts over with channel 1.

Channel 1

Channel 2

.

.

.

Channel 8

Channel 1

Scan N

Scan N+1

.

.

.

Scan N+7

Scan N+8

Scan

I/O Update

Execute Application Program

Read the data

Store data

Even though the channel updates to the CPU are synchronous with the CPU scan, the module asynchronously monitors the thermocouple signal and converts the signal to a temperature (or 12-bit binary) representation. This enables the module to continuously provide accurate measurements without slowing down the discrete control logic in the RLL program.

9–7

F3–08THM–n 8-Channel Thermocouple Input

Understanding the

I/O Assignments

You may recall the F3–08THM–n module appears to the CPU as a 16-point module.

These 16 points provide:

S an indication of which channel is active.

S the digital representation of the temperature.

Since all I/O points are automatically mapped into Register (R) memory, it is very easy to determine the location of the data word that will be assigned to the module.

F3–08THM

8pt

Relay

050

057

8pt

Output

040

047

8pt

Output

030

037

16pt

Input

8ch

(Analog)

16pt

Input

020

027

120

127

010

017

110

117

000

007

100

107

R 002, R012

MSB

1

1

7

R 011

LSB

1

1

0

R 000, R010

MSB

0

1

7

R 001

LSB

0

1

0

Active Channel

Indicator Inputs

Within these two register locations, the individual bits represent specific information about the analog signal.

Scan

N

N+1

N+2

N+3

N+4

N+5

N+6

N+7

N+8

The next to last three bits of the upper

Register indicate the active channel. The indicators automatically increment with each CPU scan.

Active Channel

Inputs Channel

000

001

010

011

100

101

110

111

000

7

8

5

6

1

3

4

1

2

MSB

R011

1

1

7

1

1

6

1

1

5

1

1

4

1

1

3

1

1

2

1

1

1

1

1

0

- active channel indicator inputs

LSB

9–8

F3–08THM–n 8-Channel Thermocouple Input

Temperature Sign

Bit

Analog Data Bits

The most significant bit is used to note the sign of the temperature. If this bit is on, then the temperature is negative. If the bit is off, then the temperature is positive.

R011

MSB

1

1

7

1

1

6

1

1

5

1

1

4

1

1

3

1

1

2

1

1

1

1

1

0

- temperature sign

LSB

The first twelve bits represent the temperature. If you have selected the

0–4095 scale, the following format is used.

Bit

3

4

5

0 (LSB)

1

2

Value

8

16

32

1

2

4

Bit

9

10

11

6

7

8

Value

64

128

256

512

1024

2048

MSB

R011 R001

LSB

1

1

7

1

1

6

1

1

5

1

1

4

1

1

3

1

1

2

1

1

1

1

1

0

0

1

7

0

1

6

0

1

5

0

1

4

0

1

3

0

1

2

0

1

1

0

1

0

- data bits

Temperature Input

Resolution

Typically, the F3–08THM–n resolution enables you to detect a 1

_

C change in temperature. The National Bureau of Standards publishes conversion tables that show how each temperature corresponds to an equivalent signal level.

Millivolt Input

Resolution

Since the module has 12-bit resolution, the analog signal is converted into 4096

“pieces” ranging from 0 – 4095 (2

12

). For example, with a –2 (100mV) module a signal of 0 mV would be 0, and a signal of

100 mV would be 4095. This is equivalent to a a binary value of 0000

0000 0000 to 1111 1111 1111, or 000 to

FFF hexadecimal. The diagram shows how this relates to the example signal range.

Each “piece” can also be expressed in terms of the signal level by using the equation shown. The following table shows the smallest signal levels that will result in a change in the data value for each signal range.

0–100 mV Scale

100mV

0 mV

0 4095

Resolution

+

H

*

L

4095

H = high limit of the signal range

L = low limit of the signal range

Range

0 – 50 mV

0 – 100 mV

Highest Signal

50 mV

100mA

Lowest Signal Smallest Change

0 mV

0mA

12.2 m

V

24.2 m

V

Now that you understand how the module and CPU work together to gather and store the information, you’re ready to write the control program.

9–9

F3–08THM–n 8-Channel Thermocouple Input

Writing the Control Program (DL330 / DL340)

Identifying the

Data Locations

Since all channels are multiplexed into a single data word, the control program must be setup to determine which channel is being read. Since the module provides input points to the CPU, it is very easy to use the channel status bits to determine which channel is being monitored.

F3–08THM

8pt

Relay

050

057

8pt

Output

8pt

Output

040

047

030

037

16pt

Input

8ch

(Analog)

16pt

Input

020

027

120

127

010

017

110

117

000

007

100

107

Automatic

Temperature

Conversion

R 002, R012 R 000, R010

R 011

MSB LSB

1

1

7

1

1

6

1

1

5

1

1

4

1

1

0

- temperature sign

- active channel indicator inputs

- data bits

MSB

0

1

7

R 001

LSB

0

1

0

If you are using the temperature scale (

°

F or

°

C) then you do not have to perform any scaling. Once you convert the binary temperature reading to a four-digit BCD number, you have the temperature.

9–10

F3–08THM–n 8-Channel Thermocouple Input

The following example shows a program designed to read any of the available channels of data into Register locations. Once the data is in a Register, you can perform math on the data, compare the data against preset values, etc. Since the

DL305 CPUs use 8-bit word instructions, you have to move the data in pieces. It’s simple if you follow the example.

Read the data

374

DSTR3

R011

F53

This rung loads the four data bits into the accumulator from Register 011 on every scan.

Temporarily store the bits to Register 501.

DOUT1

R501

F61

DSTR1

R001

F51

This rung loads the eight data bits into the accumulator from Register 001.

Store channel 1

114 115 116

Store channel 2

114 115 116

DOUT1

R500

F61

DSTR

R500

BCD

DOUT

R400

DOUT

R402

F50

F86

F60

F60

Temporarily store the bits to Register 500. Since the most significant bits were loaded into 501, now

R500 and R501 contain all twelve bits in order.

Now that all the bits are stored, load all twelve bits into the accumulator.

Math operations are performed in BCD. This instruction converts the binary data to BCD. (You can omit this step if your application does not require the conversion.)

The channel selection inputs are used to let the

CPU know which channel has been loaded into the accumulator. By using these inputs to control a

DOUT instruction, you can easily move the data to a storage register. Notice the DOUT instruction stores the data in two bytes. (Two bytes are required for four digit BCD numbers.)

Store channel 3

114 115 116

DOUT

R404

F60

Store channel 4

114 115 116

DOUT

R406

F60

Store channel 5

114 115 116

DOUT

R410

F60

Store channel 6

114 115 116

DOUT

R412

F60

Store channel 7

114 115 116

DOUT

R414

F60

Store channel 8

114 115 116

DOUT

R416

F60

F3–08THM–n 8-Channel Thermocouple Input

9–11

Using the Sign Bit

By adding a couple of simple rungs you can easily monitor the temperature for positive vs. negative readings. (For example, you have to know whether the temperature is +100

_

F or –100

_

F.) Notice how we’ve changed Channel 2 to control an output that denotes the sign of the temperature.

Read the data

374

DSTR3

R011

F53

DOUT1

R501

F61

DSTR1

R001

F51

DOUT1

R500

F61

DSTR

R500

F50

BCD F86

Store channel 1

114 115 116

DOUT

R400

F60

Store channel 2

114 115 116

DOUT

R402

F60

114 115 116 117

114 115 116 117

200

SET

200

RST

This rung loads the four data bits into the accumulator from Register 011 on every scan.

Temporarily store the bits to Register 501.

This rung loads the eight data bits into the accumulator from Register 001.

Temporarily store the bits to Register 500. Since the most significant bits were loaded into 501, now

R500 and R501 contain all twelve bits in order.

Now that all the bits are stored, load all twelve bits into the accumulator.

Math operations are performed in BCD. This instruction converts the binary data to BCD. (You can omit this step if your application does not require the conversion.)

The channel selection inputs are used to let the

CPU know which channel has been loaded into the accumulator. By using these inputs to control a

DOUT instruction, you can easily move the data to a storage register. Notice the DOUT instruction stores the data in two bytes. (Two bytes are required for four digit BCD numbers.)

If 117 is on, then the temperature on channel 2 is negative.

If 117 is off, then the temperature on channel 2 is positive.

Store channel 3

114 115 116

DOUT

R404

F60

Store channel 4

114 115 116

DOUT

R406

F60

9–12

F3–08THM–n 8-Channel Thermocouple Input

Scaling the Input

Data

If you are using the –1 (50mV) or the

–2 (100mV) versions, you may want to scale the data to represent the measurements in engineering units, which provide more meaningful data.

This is accomplished by using the conversion formula shown.

NOTE: The thermocouple versions automatically provide the correct temperature readings. Scaling is not required.

The following example shows how you would use the analog data to represent pressure (PSI) from 0 to 100. This example assumes the analog value is

1760. This should yield approximately

42.9 PSI.

Units

+

A

4096

S

Units = value in Engineering Units

A = Analog value (0 – 4095)

S = high limit of the Engineering unit range

Units

+

A

4096

S

Units

+

1760

4096

100

Units

+

42.9

F3–08THM–n 8-Channel Thermocouple Input

9–13

The following instructions are required to scale the data. (We’ll continue to use the

42.9 PSI example.) Once we’ve explained how these instructions operate, we’ll show an example program.

This example assumes you have already read the analog data and stored the BCD equivalent in R400 and R401

Scale the data

114 115 116

DSTR

R400

F50

This instruction brings the analog value (in BCD) into the accumulator.

Accumulator Aux. Accumulator

1 7 6 0 0 0 0 0

R577 R576

DIV

K4096

F74

DSTR

R576

F50

MUL

K100

F73

DSTR

R576

F50

DOUT

R450

F60

The analog value is divided by the resolution of the module, which is 4096. (1760 / 4096 = 0.4296)

Accumulator

0 0 0 0

Aux. Accumulator

4 2 9 6

R577 R576

This instruction moves the two-byte decimal portion into the accumulator for further operations.

Accumulator

4 2 9 6

Aux. Accumulator

4 2 9 6

R577 R576

The accumulator is then multiplied by the scaling factor, which is 100. (100 x 4296 = 429600). Notice the most significant digits are now stored in the auxilliary accumulator. (This is different from the way the Divide instruction operates.)

Accumulator

9 6 0 0

Aux. Accumulator

0 0

R577

4 2

R576

This instruction moves the two-byte auxilliary accumulator for further operations.

Accumulator

0 0 4 2

Aux. Accumulator

0 0 4 2

R577 R576

This instruction stores the accumulator to R450 and R451. R450 and R451 now contain the PSI, which is 42 PSI.

Accumulator

0 0 4 2

Store in R451 & R450

0 0 4 2

R451 R450

9–14

F3–08THM–n 8-Channel Thermocouple Input

You probably noticed the previous example yielded 42 PSI when the real value should have been 42.9 PSI. By changing the scaling value slightly, we can “imply” an extra decimal of precision. Notice in the following example we’ve added another digit to the scale. Instead of a scale of 100, we’re using 1000, which implies 100.0 for the

PSI range.

This example assumes you have already read the analog data and stored the BCD equivalent in R400 and R401

Scale the data

114 115 116

DSTR

R400

F50

This instruction brings the analog value (in BCD) into the accumulator.

Accumulator Aux. Accumulator

1 7 6 0 0 0 0 0

R577 R576

DIV

K4096

F74

DSTR

R576

F50

MUL

K1000

F73

DSTR

R576

F50

DOUT

R450

F60

The analog value is divided by the resolution of the module, which is 4096. (1760 / 4096 = 0.4296)

Accumulator

0 0 0 0

Aux. Accumulator

4 2 9 6

R577 R576

This instruction moves the two-byte decimal portion into the accumulator for further operations.

Accumulator

4 2 9 6

Aux. Accumulator

4 2 9 6

R577 R576

The accumulator is multiplied by the scaling factor, which is now 1000. (1000 x 4296 = 4296000). The most significant digits are now stored in the auxilliary accumulator. (This is different from the way the Divide instruction operates.)

Accumulator

6 0 0 0

Aux. Accumulator

0 4

R577

2 9

R576

This instruction moves the two-byte auxilliary accumulator for further operations.

Accumulator

0 4 2 9

Aux. Accumulator

0 4 2 9

R577 R576

This instruction stores the accumulator to R450 and R451. R450 and R451 now contains the PSI, which implies 42.9.

Accumulator

0 4 2 9

Store in R451 & R450

0 4 2 9

R451 R450

F3–08THM–n 8-Channel Thermocouple Input

9–15

This example program shows how you can use the instructions to load these equation constants into data registers. The example is written for channel 1, but you can easily use a similar approach to use different scales for all channels if required.

You may just use the appropriate constants in the instructions dedicated for each channel, but this method allows easier modifications. For example, you could easily use an operator interface or a programming device to change the constants if they are stored in Registers.

Load the constants

374

DSTR

K4096

F50

DOUT

R430

F60

DSTR

K1000

F50

DOUT

R432

F60

On the first scan, these first two instructions load the analog resolution (constant of 4096) into R430 and R431.

These two instructions load the high limit of the

Engineering unit scale (constant of 1000) into

R432 and R433. Note, if you have different scales for each channel, you’ll also have to enter the

Engineering unit high limit for those as well.

Read the data

374

DSTR3

R011

F53

DOUT1

R501

F61

This rung loads the four most significant data bits into the accumulator from Register 011 on every scan.

Temporarily store the bits to Register 501.

Store channel 1

114 115 116

DIV

R430

F74

DSTR

R576

F50

MUL

R432

F73

DSTR

R576

F50

DOUT

R400

F60

The analog value is divided by the resolution of the module, which is stored in R430 and R431.

This instruction moves the decimal portion from the auxilliary accumulator into the regular accumulator for further operations.

The accumulator is multiplied by the scaling factor, which is stored in R432 and R433.

This instruction moves most significant digits (now stored in the auxilliary accumulator) into the regular accumulator for further operations.

The scaled value is stored in R400 and R401 for further use.

9–16

F3–08THM–n 8-Channel Thermocouple Input

Writing the Control Program (DL350)

Reading Values:

Pointer Method and Multiplexing

Pointer Method

There are two methods of reading values for the DL350:

S

The pointer method (all system bases must be D3–xx–1 bases to

support the pointer method)

S

Multiplexing

You must use the multiplexing method with remote I/O modules (the pointer method will not work). You can use either method when using DL350, but for ease of programming it is strongly recommended that you use the pointer method.

The DL350 has special V-memory locations assigned to each base slot that greatly simplifies the programming requirements. These V-memory locations allow you to:

S specify the data format

S specify the number of channels to scan

S specify the storage locations

The example program shows how to setup these locations. Place this rung anywhere in the ladder program or in the Initial Stage if you are using RLL

PLUS

instructions. This is all that is required to read the data into V-memory locations.

Once the data is in V-memory, you can perform math on the data, compare the data against preset values, and so forth. V2000 is used in the example, but you can use any user V-memory location. In this example the module is installed in slot 2. You should use the V-memory locations for your module placement.

SP0

LD

K

08

00

OUT

V7662

LDA

O2000

OUT

V7672

- or -

LD

K

88

00

Loads a constant that specifies the number of channels to scan and the data format. The upper byte, most significant nibble (MSN) selects the data format (i.e. 0=BCD, 8=Binary), the LSN selects the number of channels (i.e. 1, 2, 3, 4, 5, 6, 7, 8).

The binary format is used for displaying data on some operator interfaces.

Special V-memory location assigned to slot 2 that contains the number of channels to scan.

This loads an octal value for the first V-memory location that will be used to store the incoming data. For example, the O2000 entered here would designate the following addresses.

Ch1 - V2000, Ch2 - V2001, Ch3 - V2002, Ch4 - V2003,

Ch5 – V2004, Ch6 – V2005, Ch7 – V2006, Ch8 – V2007

The octal address (O2000) is stored here. V7672 is assigned to slot

2 and acts as a pointer, which means the CPU will use the octal value in this location to determine exactly where to store the incoming data.

F3–08THM–n 8-Channel Thermocouple Input

9–17

The table shows the special V-memory locations used with the DL350. Slot 0 (zero) is the module next to the CPU, slot 1 is the module two places from the CPU, and so on. Remember, the CPU only examines the pointer values at these locations after a mode transition. The pointer method is supported on expansion bases up to a total of

8 slots away from the DL350 CPU. The pointer method is not supported in slot 8 of a

10 slot base.

Slot

Analog Input Module Slot-Dependent V-memory Locations

0 1 2 3 4 5 6 7

No. of Channels V7660 V7661 V7662 V7663 V7664 V7665 V7666 V7667

Storage Pointer V7670 V7671 V7672 V7673 V7674 V7675 V7676 V7677

9–18

F3–08THM–n 8-Channel Thermocouple Input

Multiplexing:

DL350 with a

D3–XX–1 Base

The example below shows how to read multiple channels on an F3–08THM

Thermocouple module in the X0 address slot of the D3–xx–1 base. If any expansion bases are used in the system, they must all be D3–xx–1 to be able to use this example. Otherwise, the conventional base addressing must be used.

Load the data

_On

SP1

This loads the analog data from the module.

LDF X0

K12

BCD

OUT

V1400

The BCD command converts the data to BCD format.

The scaled value is stored in V1400 with an implied decimal.

Channel 1 Select Bit States

X14 X15 X16

LD

V1400

OUT

V2000

This writes channel one data to V2000 when bits X14, X15 and X16 are as shown.

Channel 2 Select Bit States

X14 X15 X16

LD

V1400

OUT

V2001

This writes channel two data to V2001 when bits X14, X15 and X16 are as shown.

Channel 3 Select Bit States

X14 X15 X16

LD

V1400

OUT

V2002

This writes channel three data to

V2002 when bits X14, X15 and X16 are as shown.

Channel 4 Select Bit States

X14 X15 X16

LD

V1400

OUT

V2003

This writes channel four data to V2003 when bits X14, X15 and X16 are as shown.

F3–08THM–n 8-Channel Thermocouple Input

9–19

Channel 5 Select Bit States

X14 X15 X16

LD

V1400

OUT

V2004

This writes channel five data to V2004 when bits X14, X15 and X16 are as shown.

Channel 6 Select Bit States

X14 X15 X16

LD

V1400

OUT

V2005

This writes channel six data to V2005 when bits X14, X15 and X16 are as shown.

Channel 7 Select Bit States

X14 X15 X16

LD

V1400

OUT

V2006

This writes channel seven data to

V2006 when bits X14, X15 and X16 are as shown.

Channel 8 Select Bit States

X14 X15 X16

Using the Sign Bit

Channel 1 Selected

X14 X15 X16 X17

X14 X15 X16 X17

C0

SET

C0

RST

LD

V1400

OUT

V2007

This writes channel eight data to

V2007 when bits X14, X15 and X16 are as shown.

X17 is the sign bit when in module address 0.

When the sign bit is on, the sign control relay (C0) is set, causing the temperature on channel one to be negative.

When the sign bit is not true, the sign bit control bit is reset, causing the temperature on channel one to be positive.

9–20

F3–08THM–n 8-Channel Thermocouple Input

Multiplexing:

DL350 with a

Conventional

DL305 Base

The example below shows how to read multiple channels on an F3–08THM

Thermocouple module in the X20–X27 / 120 –127 address of a DL305 conventional base. The first six channels are shown.

Load the data

_On

SP1

LDF X120

This loads the upper byte of the analog data from the module.

K8

SHFL

K8

ORF X20

K8

ANDD

BCD

Kfff

This shifts the to the left to make room for the lower byte of data.

This brings the lowewr byte of data from the module into the accumulator.

Channel 1 Select Bit States

X124 X125 X126

OUT

V2200

Channel 2 Select Bit States

X124 X125 X126

LD

V2200

OUT

V3000

LD

V2200

OUT

V3001

This masks off the 12 analog data bits

The BCD command converts the data to BCD format.

The channel data is stored in V2200.

This writes channel one data to V3000 when bits X124, X125 and X126 are as shown.

This writes channel two data to V3001 when bits X124, X125 and X126 are as shown.

Channel 3 Select Bit States

X124 X125 X126

LD

V2200

OUT

V3002

This writes channel three data to

V3002 when bits X124, X125 and

X126 are as shown.

F3–08THM–n 8-Channel Thermocouple Input

9–21

Channel 4 Select Bit States

X124 X125 X126

Channel 5 Select Bit States

X124 X125 X126

LD

V2200

OUT

V3003

LD

V2200

OUT

V3004

This writes channel four data to V3003 when bits X124, X125 and X126 are as shown.

This writes channel five data to V3004 when bits X124, X125 and X126 are as shown.

Channel 6 Select Bit States

X124 X125 X126

LD

V2200

OUT

V3005

This writes channel six data to V3005 when bits X14, X15 and X16 are as shown.

Channel 1 Negative Temp

X14 X15 X16 X17

X14 X15 X16 X17

C0

SET

C0

RST

X17 is the sign bit when in module address 0.

When the sign bit is on, the sign control relay (C0) is set, causing the temperature on channel one to be negative.

When the sign bit is not true, the sign bit control bit is reset, causing the temperature on channel one to be positive.

9–22

F3–08THM–n 8-Channel Thermocouple Input

Scaling the

Input Data

Most applications usually require measurements in engineering units, which provide more meaningful data.

This is accomplished by using the conversion formula shown.

You may have to make adjustments to the formula depending on the scale you choose for the engineering units.

Units

+

A H

*

4095

L

H = high limit of the engineering unit range

L = low limit of the engineering unit range

A = Analog value (0 – 4095)

For example, if you wanted to measure pressure (PSI) from 0.0 to 99.9 then you would have to multiply the analog value by 10 in order to imply a decimal place when you view the value with the programming software or a handheld programmer.

Notice how the calculations differ when you use the multiplier.

Here is how you would write the program to perform the engineering unit conversion.

This example assumes you have BCD data loaded into the appropriate V-memory locations using instructions that apply for the model of CPU you are using.

NOTE:

This example uses SP1, which is always on. You could also use an X, C, etc. permissive contact.

SP1

LD

V3000

MUL

K1000

DIV

K4095

When SP1 is on, load channel 1 data to the accumulator.

Multiply the accumulator by 1000 (to start the conversion).

Divide the accumulator by 4095.

Store the result in V3010.

OUT

V3010

F3–08THM–n 8-Channel Thermocouple Input

9–23

Temperature and

Digital Value

Conversions

Millivolt and Digital

Value Conversions

Since the thermocouple devices are non-linear, it is much easier to rely on published standards for conversion information. The National Bureau of Standards publishes conversion tables that show how each temperature corresponds to an equivalent signal level.

Sometimes it is helpful to be able to quickly convert between the signal levels and the digital values. This is especially helpful during machine startup or troubleshooting.

The following table provides formulas to make this conversion easier.

mV Range

MV50

0 to 50 mV

MV100

0 to 100 mV

If you know the digital value ... If you know the analog signal level ...

A

+

50D

4095

D

+

4095

50

A

A

+

100D

4095

D

+

4095

100

A

For example, if you are using a

–2 (100mV) version and you have measured the signal as 30 mV, you would use the following formula to determine the digital value that should be stored in the register location that contains the data.

D

+

4095

100

A

D

+

4095

(30)

100

D

+

(40.95) (30)

D

+

1229

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