Chapter 4

Chapter 4

F3–08AD–1

8-Channel

Analog Input

In This Chapter. . . .

Ċ Module Specifications

Ċ Setting the Module Jumpers

Ċ Connecting the Field Wiring

Ċ Module Operation

Ċ Writing the Control Program

1

4

4–2

F3–08AD–1 8-Channel Analog Input

Module Specifications

Analog Input

Configuration

Requirements

The following table provides the specifications for the F3–08AD Analog 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

Conversion Time

Converter Type

Linearity Error

Maximum Inaccuracy

Accuracy vs. Temperature

Recommended Fuse

Power Budget Requirement

External Power Supply

Operating Temperature

Storage Temperature

Relative Humidity

Environmental air

Vibration

Shock

Noise Immunity

8, single ended (one common)

4 – 20 mA

12 bit (1 in 4096)

250

W

"

0.1%, 1/2W current input

"

30mA

35 m s per channel

1 channel per CPU scan

Successive Approximation, AD574

"

1 count (0.03% of full scale) maximum

0.35% of full scale at 77

°

F (25

°

C)

57 ppm /

_

C maximum full scale (including maximum offset change of 2 counts)

0.032 A, Series 217 fast-acting

25 mA @ 9 VDC, 37 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 F3–08AD Analog 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.

4–3

F3–08AD–1 8-Channel Analog Input

Setting the Module Jumpers

Jumper Locations

The module is set at the factory for a 4–20 mA signal on all eight channels. If this is acceptable you do not have to change any of the jumpers. The following diagram shows how the jumpers are set.

Channels

Selecting the

Number of

Channels

If you examine the rear of the module, you’ll notice several jumpers. The jumpers labeled +1, +2 and +4 are used to select the number of channels that will be used. Without any jumpers the module processes one channel (channel

1). By installing the jumpers you can add channels. The module is set from the factory for eight channel operation.

For example, if you install the +1 jumper, you add one channel for a total of two.

Now if you install the +2 jumper you add two more channels for a total of four.

Any unused channels are not processed so if you only select channels 1–4, then the last four channels will not be active.

The following table shows which jumpers to install.

Channel(s) +4 +2 +1

1

1 2

No

No

No

No

No

Yes

1 2 3

1 2 3 4

1 2 3 4 5

1 2 3 4 5 6

No

No

Yes No

Yes Yes

Yes No

Yes No

No

Yes

1 2 3 4 5 6 7 Yes Yes No

1 2 3 4 5 6 7 8 Yes Yes Yes

+4 +2 +1

Number of

Channels

Jumpers installed as shown selects 8-channel operation

4–4

F3–08AD–1 8-Channel Analog 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 F3–08AD receives all power from the base. A separate power supply is not required.

Current Loop

Transmitter

Impedance

Standard 4 to 20 mA transmitters and transducers can operate from a wide variety of power supplies. Not all transmitters are alike and the manufacturers often specify a minimum loop or load resistance that must be used with the transmitter.

The F3–08AD provides 250 ohm resistance for each channel. If your transmitter requires a load resistance below 250 ohms, then you do not have to make any adjustments. However, if your transmitter requires a load resistance higher than 250 ohms, then you need to add a resistor in series with the module.

Consider the following example for a transmitter being operated from a 36 VDC supply with a recommended load resistance of 750 ohms. Since the module has a

250 ohm resistor, you need to add an additional resistor.

R

+

Tr

*

Mr

R

+

750

*

250

R w

500

R – Resistor to add

Tr – Transmitter Requirement

Mr – Module resistance (internal 250 ohms)

DC Supply

0V

+36V

R

Module Channel 1

+

250W

+ –

Two-wire Transmitter

4–5

F3–08AD–1 8-Channel Analog Input

Removable

Connector

Wiring Diagram

The F3–08AD module has a removable connector to make wiring easier. Simply squeeze the top and bottom tabs and gently pull the connector from the module.

Note 1: Terminate all shields at their respective signal source

Note 2: To avoid “ground loop” errors, the following transmitter types are recommended:

2 & 3 wire: Isolation between input signal & P/S

4 wire: Full isolation between input signal, P/S and output signal.

+

-

4 wire 4-20mA

Transmitter P/S

See note

4 wire

4-20mA

4 wire

4-20mA

4 wire

4-20mA

4 wire

4-20mA

2 wire

4-20mA

2 wire

4-20mA

3 wire

4-20mA

3 wire

4-20mA

6+

5–

6–

7+

8+

7–

8–

COM

3+

4+

3–

4–

5+

1+

2+

1–

2–

+ -

External P/S for 4-20mA

Transmitters

(Switching Type DC P/S not recommended)

Internal Module Wiring

3+

4+

3–

4–

5+

6+

COM

1+

2+

1–

2–

5–

6–

7+

8+

7–

8–

COM

250

250

A/D

250

250

Analog

Switch

250

250

250

250

ANALOG INPUT

F3–08AD

+

7

+

5

+

3

+

1

4–20mA

C

O

M

+

2

+

4

+

6

+

8

C

O

M

4–6

F3–08AD–1 8-Channel Analog 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 F3–08AD 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.

You do not have to select all of the channels. Unused channels are not processed, so if you select only four channels, then the channels will be updated within four scans.

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 analog transmitter signal and converts the signal to a 12-bit binary representation. This enables the module to continuously provide accurate measurements without slowing down the discrete control logic in the RLL program.

4–7

F3–08AD–1 8-Channel Analog Input

Understanding the

I/O Assignments

You may recall the F3–08AD 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 analog signal.

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.

F3–08AD

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

R 002, R012 R 000, R010

Active Channel

Indication Inputs

R 011 R 001

MSB LSB MSB LSB

1

1

7

- not used

1

1

0

0

1

7

0

1

0

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

The next to last three bits of the upper

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

Scan Channel Inputs Active Channel

N

N+1

N+2

N+3

N+4

N+5

N+6

N+7

N+8

000

001

010

011

100

101

110

111

000

1

2

3

4

5

6

7

8

1

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

LSB

- channel indicator inputs

4–8

F3–08AD–1 8-Channel Analog Input

Analog Data Bits

The remaining twelve bits represent the analog data in binary format.

Bit

0 (LSB)

3

4

1

2

5

Value

1

8

16

2

4

32

Bit

6

9

10

7

8

11

Value

64

128

256

512

1024

2048

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 4 – 20 mA scale, a 4 mA signal would be 0, and a 20 mA signal would be 4095. This is equivalent to a binary value of 0000 0000 0000 to

1111 1111 1111, or 000 to FFF hexadecimal. The following diagram shows how this relates to each 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.

R011

MSB

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

20mA

4 – 20mA

4mA

0 4095

Resolution

+

H

*

L

4095

H = high limit of the signal range

L = low limit of the signal range

Range

4 to 20mA

Highest Signal

20mA

Lowest Signal Smallest Change

4mA 3.91 m

A

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.

4–9

F3–08AD–1 8-Channel Analog 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 active channel status bits to determine which channel is being monitored.

F3–08AD

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 R 000, R010

R 011 R 001

MSB LSB MSB LSB

Single Channel on

Every Scan

1

1

7

- not used

1

1

0

0

1

7

0

1

0

The following example shows a program that is designed to read a single channel of analog data into a Register location on every scan. Once the data is in a Register, you can perform math on the data, compare the data against preset values, etc. This example is designed to read channel 1. Since you use jumpers to select the number of channels to scan, this is the only channel that you can use in this manner.

374

DSTR1

R001

F51

This rung loads the data into the accumulator on every scan. (You can use any permissive contact.)

DOUT1

R400

F61

DSTR1

R011

F51

DOUT1

R401

F61

F50 DSTR

R400

BCD

F86

Since the active channel indicators are all off when channel 1 is being read, you would not have to use them. (Since you cannot isolate the individual channels for scanning, channel 1 is the only channel that can be used in this manner.) The

DOUT1 instruction moves the data to a storage register. The BCD value will be stored in R400 and

R401. (Two bytes are required for four digit BCD numbers.)

The DL305 CPUs perform math operations in

BCD. This instruction converts the binary data to

BCD. (You can omit this step if your application does not require the conversion.)

DOUT

R400

F60

4–10

F3–08AD–1 8-Channel Analog Input

Reading Multiple

Channels over

Alternating Scans

The following example shows a program designed to read any of the available channels of analog 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 most significant data bits into the accumulator from Register 011 on every scan. (You could use any permissive contact.)

Temporarily store the bits to Register 501.

DOUT1

R501

F61

DSTR1

R001

F51

This rung loads the eight least significant 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 indicator 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

Scaling the

Input Data

F3–08AD–1 8-Channel Analog Input

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

This is accomplished by using the conversion formula shown.

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

4–11

Units

+

1760

4096

100

Units

+

42.9

4–12

F3–08AD–1 8-Channel Analog Input

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

42.9 PSI example. In this example we’re using channel 1. Input 114, input 115, and input 116 are all off when channel 1 data is being read. Of course, if you were using a different channel, you would use the active channel indicator point combination that corresponds to the channel you were using.

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

F3–08AD–1 8-Channel Analog Input

4–13

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 contain the PSI, which implies 42.9.

Accumulator

0 4 2 9

Store in R451 & R450

0 4

R451

2 9

R450

4–14

F3–08AD–1 8-Channel Analog Input

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

You could 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. (You could use any permissive contact.)

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.

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.

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.

F3–08AD–1 8-Channel Analog Input

4–15

Writing the Control Program (DL350)

Reading Values:

Pointer Method and Multiplexing

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.

NOTE: Do not use the pointer method and the PID PV auto transfer from I/O module function together for the same module. If using PID loops, use the pointer method and ladder logic code to map the analog input data into the PID loop table.

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.

4–16

F3–08AD–1 8-Channel Analog Input

Multiplexing:

DL350 with a

Conventional

DL305 Base

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.

Analog Input Module Slot-Dependent V-memory Locations

Slot 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

The example below shows how to read multiple channels on an F3–08AD Analog module in the X20–27 / X120–127 address slot. This module must be placed in a 16 bit slot in order to work.

Load the data

_On

SP1

LDF X120

K8

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

SHFL

ORF

ANDD

BCD

K8

X20

K8

Kfff

SHFL K8 shifts the data to the left eight places to make room for the lower byte of data.

The ORF X20 brings the lower byte of data from the module into the accumulator. At this time there is a full word of data from the analog module in the accumulator.

The ANDD Kfff masks off the twelve least significant bits of data from the word. This is the actual analog value.

The BCD command converts the data to BCD format.

Channel 1 Select Bit States

X124 X125 X126

OUT

V3000

Channel 2 Select Bit States

X124 X125 X126

OUT

V3001

Channel 3 Select Bit States

X124 X125 X126

OUT

V3002

example continued on next page

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

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

This writes channel three analog data to V3002 when bits X124, X125 and X126 are as shown.

F3–08AD–1 8-Channel Analog Input

4–17 example continued from previous page

Channel 4 Select Bit States

X124 X125 X126

OUT

V3003

Channel 5 Select Bit States

X124 X125 X126

OUT

V3004

Channel 6 Select Bit States

X124 X125 X126

OUT

V3005

Channel 7 Select Bit States

X124 X125 X126

OUT

V3006

Channel 8 Select Bit States

X124 X125 X126

OUT

V3007

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

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

This writes channel six analog data to V3005 when bits X124, X125 and X126 are as shown.

This writes channel seven analog data to V3006 when bits X124, X125 and X126 are as shown.

This writes channel eight analog data to V3007 when bits X124, X125 and X126 are as shown.

4–18

F3–08AD–1 8-Channel Analog Input

Multiplexing:

DL350 with a

D3–xx–1 Base

The example below shows how to read multiple channels on an F3–08AD Analog module in the X0 address slot of a 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

LD

VX0

This rung loads the only the channel select bits into V1400. The SHFR shifts the analog data out of the word.

SHFR

K12

OUT

V1400

_On

SP1

LDF X0

K12

BCD

This rung loads the only the analog input data and converts it to BCD.

Channel 1

V1400

=

K0

OUT

V3000

Channel 2

V1400

=

K1

OUT

V3001

Channel 3

V1400

=

K2

OUT

V3002

example continued on next page

These rungs store the BCD analog input data into consecutive V memory registers. V1400 will increment once per scan from 0 to 7.

F3–08AD–1 8-Channel Analog Input

4–19 example continued from previous page

Channel 4

V1400

=

K3

OUT

V3003

Channel 5

V1400

=

K4

OUT

V3004

Channel 6

V1400

=

K5

OUT

V3005

Channel 7

V1400

=

Channel 8

K6

OUT

V3006

V1400

=

K7

OUT

V3007

These rungs store the BCD analog input data into consecutive V memory registers. V1400 will increment once per scan from 0 to 7.

4–20

F3–08AD–1 8-Channel Analog 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

OUT

V3010

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.

Analog and Digital

Value Conversions

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.

Range

4 to 20mA

If you know the digital value ...

If you know the analog signal level ...

A

+

16D

4095

)

4 D

+

4095

16

(A

*

4)

For example, if you have measured the signal at 10mA, 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

16

(A

*

4)

D

+

4095

16

(10mA

*

4)

D

+

(255.93) (6)

D

+

1536

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