F2-08AD-1

8-Channel Analog

Current Input

In This Chapter. . . .

— Module Specifications

— Setting the Module Jumpers

— Connecting the Field Wiring

— Module Operation

— Writing the Control Program

4

4--2

F2-08AD-1 8-Channel Analog Current Input

Module Specifications

NOTE: A re--designed F2--08AD--1 with a single circuit board design was released in 2009.

The jumper link location is different. See Setting the Module Jumpers on page 4--5. Also, some specifications were changed on page 4--3. Otherwise, the re--designed module functions the same as the prior design.

The F2-08AD-1 Analog Input module provides several hardware features:

S

Analog inputs are optically isolated from the PLC logic.

S

On-board 250 ohm, 1/2 watt precision resistors provide substantial over-current-protection for 4--20mA current loops.

S

The module has a removable terminal block so the module can be easily removed or changed without disconnecting the wiring.

S

With a DL240, DL250--1 and

DL260 CPU, you can read all channels in one scan.

Firmware Requirements:

To use this module, D2--230 CPUs must have firmware version 1.6 or later. To use the pointer method of writing values,

D2--240 CPUs require firmware version

2.2 or later.

All versions of the D2--250--1 and

D2--260 CPU’s firmware support this module and the pointer method.

IN

F2--08AD-1

10--30VDC

5mA

0V

+24V

CH1+

CH2+

CH3+

CH4+

CH5+

CH6+

CH7+

CH8+

ANALOG IN

4--20mA

ANALOG

8CH

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--3

F2-08AD-1 8-Channel Analog Current Input

Input

Specifications

The following tables provide the specifications for the F2--08AD--1 Analog Input

Module. Review these specifications to make sure the module meets your application requirements.

Number of Channels

Input Range

Resolution

Step Response

Crosstalk

Active Low--Pass Filtering

Input Impedance

8, single ended (one common)

4 to 20 mA current

12 bit (1 in 4096)

1 ms (*7 ms) to 95% of full step change

--70 dB, 1 count maximum

--3dB @ 200Hz (-6 dB per octave)

250Ω 0.1%, ½W current input

Input Stability

Full Scale Calibration Error

(Offset Error Included)

1 count

.1% @ 25 C

.25% 0 to 60_C (32 to 140F)

50 ppm/ C maximum full scale calibration

(including maximum offset change)

General

Specifications

One count in the specification table is equal to one least significant bit of the analog data value (1 in

4096).

PLC Update Rate

Data Acquisition Time

Digital Inputs

Input Points Required

1 channel per scan maximum (DL230 CPU)

8 channels per scan maximum (DL240/250--1/260 CPU)

3ms/channel (asynchronous)

12 binary data bits, 3 channel ID bits, 1 broken transmitter detection bit

16 point (X) input module

External Power Supply 5 mA (*80 mA) maximum, 10--30 VDC (*18--26.4 VDC)

Storage Temperature

Relative Humidity

Environmental air

Vibration

Shock

--20 to 70_ C (--4 to 158 F)

5 to 95% (non-condensing)

No corrosive gases permitted

MIL STD 810C 514.2

MIL STD 810C 516.2

Noise Immunity NEMA ICS3--304

* Values in parenthesis with an asterisk are for older modules with two circuit board design and date codes 0609B5 and previous. Values not in parenthesis are for single circuit board models with date code 0709C1 and above.

Analog Input

Configuration

Requirements

The F2-08AD-1 Analog Input appears as a 16-point discrete input module. The module can be installed in any slot of a DL205 system. The available power budget and discrete I/O points are the limiting factors. Check the user manual for your particular model of CPU and I/O base for more information regarding power budget and number of local, local expansion or remote I/O points.

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--4

F2-08AD-1 8-Channel Analog Current Input

Special

Placement

Requirements

(DL230 and

Remote I/O Bases)

Even though the module can be placed in any slot, it is important to examine the configuration if you are using a DL230 CPU. As you will see in the section on writing the program, you use V-memory locations to extract the analog data. If you place the module so that the input points do not start on a V-memory boundary, the instructions cannot access the data. This also applies when placing this module in a remote base using a D2--RSSS in the CPU slot.

Correct!

F2-08AD-1

Data is correctly entered so input points start on a V-memory boundary.

Slot 0

8pt

Input

X0

--

X7

Slot 1

8pt

Input

X10

--

X17

MSB

X

3

7

V40400

Slot 2

16pt

Input

X20

--

X37

Slot 3

16pt

Input

X40

--

X57

Slot 4

16pt

Output

Y0

--

Y17

V40401

V40402

LSB

X

2

0

Incorrect

F2-08AD-1

Slot 0

8pt

Input

X0

--

X7

Slot 1

16pt

Input

X10

--

X27

Slot 2

16pt

Input

X30

--

X47

Slot 3

16pt

Input

X50

--

X67

Slot 4

16pt

Output

Y0

--

Y17

Data is split over two locations, so instructions cannot access data from a DL230.

MSB

V40401

LSB MSB

V40400

LSB

X

3

7

X

3

0

X

2

7

X

2

0

X

1

7

X

1

0

X

7

X

0

To use the V-memory references required for a DL230 CPU, the first input address assigned to the module must be one of the following X locations. The table also shows the V-memory addresses that correspond to these X locations.

X X0 X20 X40 X60 X100 X120 X140 X160

V V40400 V40401 V40402 V40403 V40404 V40405 V40406 V40407

DL205 Analog Manual 7th Ed. Rev. B 4/10

F2-08AD-1 8-Channel Analog Current Input

Setting the Module Jumpers

Selecting the

Number of

Channels

There are three jumpers, labeled +1, +2, and +4 that are used to select the number of channels that will be used.

See the figures below to locate the jumpers on your module. The module is set from the factory for eight channel operation (all three jumpers installed).

Any unused channels are not processed. For example, if you only select channels 1 thru 3, channels 4 thru

8 will not be active. The following table shows how to set the jumpers to select the number of channels.

No. of

Channels +1 +2 +4

1

1,2

1,2,3

1,2,3,4

No No

Yes No

No

No

No Yes No

Yes Yes No

1,2,3,4,5

1,2,3,4,5,6

No No

Yes No

Yes

Yes

1,2,3,4,5,6,7 No Yes Yes

1,2,3,4,5,6,7,8 Yes Yes Yes

For example, to select 8-channel operation, leave all three jumpers installed. To select only channel 1, remove (or store on a single post to prevent losing them) all three jumpers.

Yes = jumper installed

No = jumper removed

4--5

Jumper Location on Modules Having

Date Code 0609B9 and Previous

(Two Circuit Board Design)

+1 +2 +4

Jumper Location on Modules Having

Date Code 0709C1 and Above

(Single Circuit Board Design)

+1+2+4

+4

+2

+1

These jumpers are located on the motherboard, the one with the black

D-shell style backplane connector.

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--6

F2-08AD-1 8-Channel Analog Current 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 transmitter source. Do

not ground the shield at both the module and the source.

S

Do not 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 F2-08AD-1 requires at least one field-side power supply. You may use the same or separate power sources for the module supply and the current transmitter supply. The module requires 18--26.4VDC, at 80 mA.

The DL205 bases have built-in 24 VDC power supplies that provide up to 300mA of current . You may use this instead of a separate supply if you are using only a couple of analog modules.

It is desirable in some situations to power the transmitters separately in a location remote from the PLC. This will work as long as the transmitter supply meets the voltage and current requirements, and the transmitter minus (--) side and the module supply’s minus (--) side are connected together.

Current Loop

Transmitter

Impedance

WARNING: If you are using the 24 VDC base power supply, make sure you calculate the power budget. Exceeding the power budget can cause unpredictable system operation that can lead to a risk of personal injury or damage to equipment.

The DL205 base has a switching type power supply. As a result of switching noise, you may notice 3--5 counts of instability in the analog input data if you use the base power supply. If this is unacceptable, you should try one of the following.

1. Use a separate linear power supply.

2. Connect the 24VDC common to the frame ground, which is the screw terminal marked “G” on the base.

By using these methods, the input stability is rated at 1 count.

If you want to use a separate supply, choose one that meets the following requirements: 18--26.4 VDC, 80mA current.

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 F2-08AD-1 provides 250 ohm resistance for each channel. If your transmitter requires a load resistance below 250 ohms, you do not have to make any adjustments. However, if your transmitter requires a load resistance higher than

250 ohms, you need to add a resistor in series with the module.

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--7

F2-08AD-1 8-Channel Analog Current Input

Consider the following example for a transmitter being operated from a 30 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 ≥ 500

R -- resistor to add

Tr -- Transmitter Requirement

Mr -- Module resistance (internal 250 ohms)

Two-wire Transmitter

+ --

Module Channel 1

DC Supply

+30V

0V

R

CH1+

CH1--

0V

250 ohms

Wiring Diagram

The F2-08AD-1 module has a removable connector to make wiring easier. Simply squeeze the top and bottom retaining clips and gently pull the connector from the module. Use the following diagram to connect the field wiring. The diagram shows separate module and transmitter power supplies. If you desire to use only one field-side supply, just combine the supplies’ positive (+) terminals into one node, and remove the transmitter supply.

Module Supply

+

18-26.4VDC

--

Typical User Wiring

Internal

Module

Wiring

IN ANALOG

8CH

See NOTE 1

-+

CH1

4--wire

4--20mA

Transmitter

+

CH2

3--wire

4--20mA

Transmitter

--

+

--

+

CH3

2-wire

4--20mA

Transmitter

--

+

CH4

2-wire

4--20mA

Transmitter

--

+

Fuse

Fuse

Fuse

Fuse

0 VDC

CH1+

CH3+

CH5+

CH7+

+24 VDC

CH2+

CH4+

CH6+

CH8+

250



250 

250 

250 

250 

250 

250 

250 

+5V

+15V

0V

--15V

A to D

Converter

F2--08AD-1

10--30VDC

5mA

0V

+24V

CH1+

CH2+

CH3+

CH4+

CH5+

CH6+

CH7+

CH8+

ANALOG IN

4--20mA

+

--

Transmitter

Supply

OV

NOTE 1: Shields should be grounded at the signal source.

NOTE 2: More than one external power supply can be used, provided all the power supply commons are connected.

NOTE 3: A Series 217, 0.032A fast-acting fuse is recommended for 4--20 mA current loops.

NOTE 4: If the power supply common of an external power supply is not connected to the 0V terminal on the module, then the output of the external transmitter must be isolated. To avoid “ground loop” errors, recommended 4--20 mA transmitter types are:

-- For 2 or 3 wire connections: Isolation between the input supply signal and the power supply.

-- For 4 wire connections:

‘

Isolation between the input supply signal, the power supply, and the 4--20 mA output.

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--8

F2-08AD-1 8-Channel Analog Current Input

Module Operation

Channel

Scanning

Sequence for a

DL230 CPU

(Multiplexing)

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 F2-08AD-1 module can supply different amounts of data per scan, depending on the type of CPU you are using. The DL230 can obtain one channel of data per

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. Unused channels are not processed, so if you select only two channels, then each channel will be updated every other scan. The multiplexing method can also be used for DL240/250--1/260 CPUs.

Scan

Read Inputs

Execute Application Program

Read the data

Store data

Scan N

Scan N+1

(repeat for ch. 3--6)

Scan N+6

Scan N+7

Scan N+8

Write to Outputs

System With

DL230 CPU

Channel 1

Channel 2

Channel 7

Channel 8

Channel 1

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--9

F2-08AD-1 8-Channel Analog Current Input

Channel Scanning

Sequence with a DL240, DL250--1 or DL260 CPU

(Pointer Method)

If you are using a DL240/250--1/260 CPU, you can obtain all eight channels of input data in one scan. This is because the DL240, DL250--1 and DL260 CPUs support special V-memory locations that are used to manage the data transfer (this is discussed in more detail in the section on Writing the Control Program.)

Scan

Read Inputs

System With

DL240/250--1/

260CPU

Execute Application Program

Read the data

Store data

Scan N

Scan N+1

Scan N+2

Scan N+3

Scan N+4

Ch 1, 2, 3, ...8

Ch 1, 2, 3, ...8

Ch 1, 2, 3, ...8

Ch 1, 2, 3, ...8

Ch 1, 2, 3, ...8

Write to Outputs

Analog Module

Updates

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.

For the vast majority of applications, the values are updated much faster than the signal changes. However, in some applications the update time can be important.

The module takes approximately 7mS to sense 95% of the change in the analog signal.

Note, this is not the amount of time required to convert the signal to a digital representation. The conversion to the digital representation takes only a few microseconds. Many manufacturers list the conversion time, but it is the settling time of the filter that really determines the update time.

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--10

F2-08AD-1 8-Channel Analog Current Input

Understanding the Input

Assignments

You may recall the F2-08AD-1 module requires 16 discrete input points in the CPU.

You can use these points to obtain:

S an indication of which channel is active.

S the digital representation of the analog signal.

S module diagnostic information.

Since all input points are automatically mapped into V-memory, it is very easy to determine the location of the data word that will be assigned to the module.

F2-08AD-1

Slot 0

8pt

Input

X0

--

X7

V40400

Slot 1

8pt

Input

X10

--

X17

MSB

Slot 2

16pt

Input

X20

--

X37

Slot 3

16pt

Input

X40

--

X57

Slot 4

16pt

Output

Y0

--

Y17

V40402 V40500

V40401

LSB

X

3

7

X

3

6

X

3

5

X

3

4

Data Bits

X

2

0

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

Analog Data Bits

2

3

0

1

4

5

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

Bit Value Bit Value

16

32

4

8

1

2

10

11

8

9

6

7

64

128

256

512

1024

2048

V40401

MSB LSB

1

5

1

4

1

3

1

2

1

1

1

0

9 8 7 6 5 4 3 2 1 0

= data bits

DL205 Analog Manual 7th Ed. Rev. B 4/10

F2-08AD-1 8-Channel Analog Current Input

Active Channel

Indicator Inputs

N

N+1

N+2

N+3

N+4

N +5

N +6

N +7

Three of the inputs are binary-encoded to indicate the active channel.

(Remember, the V-memory bits are mapped directly to discrete inputs.) The inputs are automatically turned on and off to indicate the active channel for each scan.

Scan X34 X35 X36 Channel

Off Off

On Off

Off On

On On

Off Off

On Off

Off On

On On

On

On

On

On

Off

Off

Off

Off

7

8

5

6

3

4

1

2

Module

Diagnostic

Inputs

The last input (X37 in this example) is the broken transmitter and missing 24 volts input power indicator.

When X37 is on, the input transmitter maybe broken for the corresponding input.

If there is no external 24 volts input power, or if there is a loose or missing terminal block, then X37 goes on and a value of zero is returned for all enabled channels.

V40401

MSB

X

3

6

X

3

5

X

3

4

= channel inputs

V40401

MSB

X

3

7

= diagnostic inputs

Module

Resolution

Since the module has 12-bit resolution, the analog signal is converted into 4096 counts ranging from 0 -- 4095 (2

12

). For example, a 4mA signal would be 0 and a

20mA signal 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 signal range.

Each count can also be expressed in terms of the signal level by using the equation shown.

20mA

4 -- 20mA

4mA

0 4095

H = high limit of the signal range

L = low limit of the signal range

16mA / 4095 = 3.907A per count

LSB

X

2

0

LSB

X

2

0

4--11

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--12

F2-08AD-1 8-Channel Analog Current Input

Writing the Control Program

Reading Values:

Pointer Method and Multiplexing

Pointer Method



230



240



250--1



260

There are two methods of reading values:

S

The pointer method

S

Multiplexing

You must use the multiplexing method when using a DL230 CPU. You must also use the multiplexing method with remote I/O modules (the pointer method will not work). You can use either method when using DL240, DL250--1 and DL260 CPUs, but for ease of programming it is strongly recommended that you use the pointer method.

The DL205 series has special V-memory locations (shown in the tables on the next page) that are assigned to each base slot that greatly simplify 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

NOTE: DL240 CPUs with firmware release 2.2 or later supports this method.

DL250 CPUs with firmware release version 1.06 or later support this method. If you must use the DL230 example, module placement in the base is very important.

Review the section earlier in this chapter for guidelines.

The example program below 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. The pointer method automatically converts values to BCD.

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. The DL230/240 CPUs do not support binary math functions, whereas the DL250 does.

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, Ch 4 - 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.

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--13

F2-08AD-1 8-Channel Analog Current Input

The tables below show the special V-memory locations used by the DL240,

DL250--1 and DL260 for the CPU base and local expansion base I/O slots. Slot 0

(zero) is the module next to the CPU or D2--CM module. Slot 1 is the module two places from the CPU or D2--CM, and so on. Remember, the CPU only examines the pointer values at these locations after a mode transition. Also, if you use the DL230

(multiplexing) method, verify that these addresses in the CPU are zero.

The Table below applies to the DL240, DL250--1 and DL260 CPU base.

CPU 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 Table below applies to the DL250--1 or DL260 expansion base 1.

Expansion Base D2--CM #1: Analog Input Module Slot-Dependent V-memory Locations

Slot 0 1 2 3 4 5 6 7

No. of Channels V36000 V36001 V36002 V36003 V36004 V36005 V36006 V36007

Storage Pointer V36010 V36011 V36012 V36013 V36014 V36015 V36016 V36017

The Table below applies to the DL250--1 or DL260 expansion base 2.

Expansion Base D2--CM #2: Analog Input Module Slot-Dependent V-memory Locations

Slot 0 1 2 3 4 5 6 7

No. of Channels V36100 V36101 V36102 V36103 V36104 V36105 V36106 V36107

Storage Pointer V36110 V36111 V36112 V36113 V36114 V36115 V36116 V36117

The Table below applies to the DL260 CPU expansion base 3.

Expansion Base D2--CM #3: Analog Input Module Slot-Dependent V-memory Locations

Slot 0 1 2 3 4 5 6 7

No. of Channels V36200 V36201 V36202 V36203 V36204 V36205 V36206 V36207

Storage Pointer V36210 V36211 V36212 V36213 V36214 V36215 V36216 V36217

The Table below applies to the DL260 CPU expansion base 4.

Expansion Base D2--CM #4: Analog Input Module Slot-Dependent V-memory Locations

Slot 0 1 2 3 4 5 6 7

No. of Channels V36300 V36301 V36302 V36303 V36304 V36305 V36306 V36307

Storage Pointer V36310 V36311 V36312 V36313 V36314 V36315 V36316 V36317

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--14

F2-08AD-1 8-Channel Analog Current Input

Reading Values

Multiplexing



230



240



250--1



260

The DL230 CPU does not have the special V-memory locations that allow you to automatically enable the data transfer. 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 appears as X input points to the CPU, it is very easy to use the active channel status bits to determine which channel is being monitored.

Note, this example is for a module installed as shown in the previous examples. The addresses used would be different if the module was installed in another I/O configuration. You can place these rungs anywhere in the program or if you are using stage programming place them in a stage that is always active.

SP1

LD

V40401

ANDD

KFFF

BCD

Loads the complete data word into the accumulator. The V-memory location depends on the I/O configuration. See Appendix A for the memory map.

This instruction masks the channel identification bits. Without this, the values used will not be correct so do not forget to include it.

It is usually easier to perform math operations in

BCD, so it is best to convert the data to BCD immediately. You can leave out this instruction if your application does not require it.

Store Channel 1

X34 X35 X36

OUT

V2000

When X34, X35 and X36 are off, channel 1 data is stored in V2000.

Store Channel 2

X34 X35 X36

OUT

V2001

When X34 is on, X35 and X36 are off, and broken transmitter detect is off, channel 2 data is stored in V2001.

(repeat for channels 3 -- 6)

Store Channel 7

X34 X35 X36

OUT

V2006

When X35 and X36 are on and X34 is off, channel 7 data is stored in V2006.

Store Channel 8

X34 X35 X36

OUT

V2007

When X34, X35 and X36 are on, channel 8 data is stored in V2007.

DL205 Analog Manual 7th Ed. Rev. B 4/10

4--15

F2-08AD-1 8-Channel Analog Current Input

Single

Channel

Selected

Analog Power

Failure

Detection

Since you do not have to determine which channel is selected, the single channel program is even more simple.

Store Channel 1

X36 X34 X35

LD

V40401

BCD

OUT

V2000

Loads the complete data word into the accumulator. The V-memory location depends on the I/O configuration. See Appendix A for the memory map.

This instruction masks the channel identification bits. Without this, the values used will not be correct, so do not forget to include it.

It is usually easier to perform math operations in BCD, so it is best to convert the data to BCD immediately. You can leave out this instruction if your application does not require it.

When X34, X35 and X36 are off, channel 1 data is stored in V2000.

The analog module has an on-board processor that can diagnose analog input circuit problems. You can easily create a simple ladder rung to detect these problems. This rung shows an input point that would be assigned if the module I/O begins at X20 as shown in the previous examples. A different point would be used if the module was installed in a different I/O arrangement.

Multiplexing method

V2000

=

K0 X37

C1

OUT

V-memory location V2000 holds channel 1 data. When a data value of zero is returned and input X37 is on, then the analog circuitry is not operating properly.

Pointers method

V2000 K8000

=

C1

OUT

V-memory location V2000 holds channel 1 data. When a data value of 8000 is returned, then the analog circuitry is not operating properly.

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.

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.

DL205 Analog Manual 7th Ed. Rev. B 4/10

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F2-08AD-1 8-Channel Analog Current Input

Analog value of 2024, slightly less than half scale, should yield 49.4 PSI

Example without multiplier Example with multiplier

Analog and

Digital Value

Conversions

Units = 49

Handheld Display

V 2001 V 2000

0000 0049

Units = 494

Handheld Display

V 2001 V 2000

0000 0494

This value is more accurate.

Here is how you would write the program to perform the engineering unit conversion. Note, this example will work with all DL205 CPUs, but it assumes you have already loaded the BCD data 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

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

MUL

K1000

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

DIV

K4095

Divide the accumulator by 4095.

OUT

V2010

Store the result in V2010.

Sometimes it is useful 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...

4

If you know the analog signal level...

(A − 4)

For example, if you have measured the signal as 10mA, you can use the formula to easily determine the digital value that will be stored in the V-memory location that contains the data.

(A − 4)

(10mA – 4)

D = (255.93) (6)

D = 1536

DL205 Analog Manual 7th Ed. Rev. B 4/10

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F2-08AD-1 8-Channel Analog Current Input

Filtering Input

Noise (DL250--1,

DL260 CPU Only)



230



240



250--1



260

Add the following logic to filter and smooth analog input noise in DL250--1 and

DL260 CPUs. This is especially useful when using PID loops. Noise can be generated by the field device and/or induced by field wiring.

The analog value in BCD is first converted to a binary number because there is not a

BCD-to-real conversion instruction. Memory location V1400 is the designated workspace in this example. The MULR instruction is the filter factor, which can be from 0.1 to 0.9. The example uses 0.2. A smaller filter factor increases filtering. You can use a higher precision value, but it is not generally needed. The filtered value is then converted back to binary and then to BCD. The filtered value is stored in location V1402 for use in your application or PID loop.

NOTE: Be careful not to do a multiple number conversion on a value. For example, if you are using the pointer method to get the analog value, it is in BCD and must be converted to binary. However, if you are using the conventional method of reading analog and are masking the first twelve bits, then it is already in binary and no conversion using the BIN instruction is needed.

SP1

BIN

BTOR

Loads the analog signal, which is a BCD value and has been loaded from V-memory location

V2000, into the accumulator. Contact SP1 is always on.

Converts the BCD value in the accumulator to binary. Remember, this instruction is not needed if the analog value is originally brought in as a binary number.

Converts the binary value in the accumulator to a real number.

SUBR

V1400

ADDR

V1400

OUTD

V1400

RTOB

BCD

OUT

V1402

Subtracts the real number stored in location

V1400 from the real number in the accumulator, and stores the result in the accumulator. V1400 is the designated workspace in this example.

Multiplies the real number in the accumulator by 0.2 (the filter factor), and stores the result in the accumulator. This is the filtered value.

Adds the real number stored in location V1400 to the real number filtered value in the accumulator, and stores the result in the accumulator.

Copies the value in the accumulator to location V1400.

Converts the real number in the accumulator to a binary value, and stores the result in the accumulator.

Converts the binary value in the accumulator to a BCD number. Note: The BCD instruction is not needed for PID loop PV (loop PV is a binary number).

Loads the BCD number filtered value from the accumulator into location V1402 to use in your application or PID loop.

DL205 Analog Manual 7th Ed. Rev. B 4/10