Created Date: November 11,2002

Created by: cdobis

This is probably really easy and I am making it harder than it should be, but I can't seem to read my analog input values from an F2-04AD-2. I am using some 7B modules to give me 0-10 volt inputs. I have a DL205 with a 260 CPU. This Analog input module is in the first (0) slot, next to the CPU. Can you help me with the programming basics in DSoft and scaling this signal? I can't seem to find a simple example of this.

TIA

Craig

Created Date: November 11,2002

Created by: marksji

On the first PLC scan you need a rung of logic that sets how many channels you want to read, what data format you want to use, and where the analog data should be stored in VMEM. You can use the special contact SP0 as the control logic for the rung. For example:

SP0---------LD K0400

OUT V7660

LDA O2000

OUT V7670

This would set BCD data to be stored in VMEM locations v2000 through v2003. If you want binary data change the K0400 to K8400. V7660 & V7670 are special VMEM locations for slot 0, if you move the card to slot x then use V766x & V767x.

This is all in the manual for the card which can be downloaded from ADs site.

Created Date: November 11,2002

Created by: showsys

I have successfully been able to get the numbers in binary and bcd using the ladder example, but my biggest difficulty is in understanding if I need to look at 2 vmem locations per channel.

I am using a DL250-1 and a F2-04THM with an EZ-Touch mono display.

I cannot seem to get a stable reading from the J-type thermocouples that we 're using. We 've played with the possibilities of chamging jumper settings, but or thermocouple vendor insists the specs meet the settings we 've seen as factory default.

The range seems off, which leads me to wonder if we need to display and calculate using both vmem locations (v2000, and v2001 in the example)

We may also have issues with improperly spec'd thermocouple wire. It appears to be unshielded over a distance of 10-15 meters.

Any suggestions would be appreciated.

TJ

Created Date: November 11,2002

Created by: cdobis

I appreciate the help, but the data in the book for the module leaves a newby like myself, still scratching his head. I have themocouples and a shunt going into 7B modules to convert my signals to 0-10v for my analog input module. There is where I run into trouble. My 7B module's range is -100 C to +300 C, 0 - 10 volts output respectively, for the thermocouple. Now, do I leave it in binary form, convert it to a real number, and where do I do the math? I need a math example, I think, just to get me going on this.

Thanks!

Created Date: November 11,2002

Created by: Tom Jenkins

For any unit conversion on any PLC you can use four function math with the following, which assumes integer math:

DataOffset = Data in input register at 4 mA (or zero analog signal of whatever range - for example 0 VDC on a 0-10 VDC transmitter)

DataSPan = Data at 10 VDC - Data @ 0 VDC

FACTOR = arbitrary factor (multiple of 10) needed to get proper resolution and accuracy

EU = Engineering Units x FACTOR

EUOffset = Engineering Units @ 0VDC x FACTOR

EUSpan = (Engineering Units @ 10VDC - Engineering Units @ 0VDC) x FACTOR

DATA = Actual data reading in input register

EU = ((EUSpan x (DATA - DataOffset))/DataSpan) + EUOffset

ProcessValue = EU / FACTOR

Example,-100 to 300 °C from 0-10 VDC with resolution of 0.1°F:

FACTOR = 10

Data @ 0 VDC = 0

Data @ 10 VDC = 4095

DataOffset = 0

DataSpan = 4095 - 0 = 4095

EUOffset = -100 x 10 = -1000

EUSpan = (300 - (-100)) x 10 = 4000

DATA = 2048

EU = ((4000 x (2048 - 0)) / 4095) + -1000 = 1000

Process Value = 1000 / 10 = 100.0 °F

One problem you will have is that the integer math for the DirectLogic PLCs isn't friendly to negative math. Because your temperature transmitter starts at -100 you can't avoid this problem. There are two solutions. One is to use floating point math - not always the best answer for a novice. The better solution is probably to have two sets of math rungs. If the raw data is below 25% (1024) use one set. If it is above 1024 use the other. Then you can avoid negative numbers. You will have to set a bit to indicate if the temperature is above or below zero.

There are lots of math examples in the manuals. Try programming first with known values, then convert to the logic needed for the temperature.

Created Date: November 11,2002

Created by: Tech Guy

Here is a program that will do what Tom's post implies. This example assumes that all data is in signed binary format. This can be imported by Directsoft version 4.0 only. To import, start at the PLC 250(-1) line and select to #END. Save this as a text file with no formatting. In Directsoft v4 Go to File -> Import. Pick the text file that you saved and give it a project name.

PLC 250(-1)

// Rung 1

// Address 0

#BEGIN COMMENT

"This program will do a zero and full scale calibration and scaling of a V-memory location "

"according to the straight line equation: "

" "

"SV=((Iv-Cfs)*(Dfs-Dz))/(Cfs-Cz)-b+Dz "

" "

"b=(Dz-(Dfs-Dz))/(Cfs-Cz) "

" "

"SV=Scaled Value "

"Iv = Input value (Number to be calibrated & scaled) "

"Dz = Device Zero "

"Dfs = Device Full Scale "

"Cz = Plc Counts at Device Zero "

"Cfs = Plc Counts at Device Full Scale "

" "

"The following example assumes that the zero and full scale values will be entered via a "

"data view into V-memory addresses v2000-v2006. IE. 5-25psi device that reads 300 "

"counts at 5psi and 4015 counts at 25 psi; "

"V2000=5, V2002=25, V2004=300, V2006=4015. "

" "

"** Solve for b ** "

#END

STR SP1

LD V2002

SUBB V2000

OUT V2020

// Rung 2

// Address 4

STR SP1

LD V2006

SUBB V2004

OUT V2022

// Rung 3

// Address 8

STR SP1

LD V2000

SUBB V2020

INV

ADDB K1

ANDD Kffff

DIVB V2022

OUT V2010

// Rung 4

// Address 17

#BEGIN COMMENT

" "

"** Now Solve for SV ** "

" "

" "

" "

#END

STR SP1

LD V2100

SUBB V2004

MULB V2020

DIVB V2022

ADDB V2010

ADDB V2000

OUT V2200

// Rung 5

// Address 25

END

// Rung 6

// Address 26

NOP

#BEGIN ELEMENT_DOC

"V2000 ", " ", " ", "Device Zero "

"V2002 ", " ", " ", "Device Fullscale "

"V2004 ", " ", " ", "PLC Counts - Zero "

"V2006 ", " ", " ", "PLC Counts - Fullscale "

"V2010 ", " ", " ", "b = (V2000-(V2002-V2000) / (V2004-V2006) "

"V2020 ", " ", " ", "Device Range "

"V2022 ", " ", " ", "Count Range "

"V2100 ", " ", " ", "Value to be Scaled and Calibrated "

"V2200 ", " ", " ", "Scaled Value "

#END

Created Date: November 12,2002

Created by: marksji

showsys,

Thermocouples are inherently unstable in most situations and need filtering. I say they are unstable in most situations because the input signal your dealing with is in the milivolt range. At those voltages it doesn't take much to generate interfearance from other AC lines that are nearby. As far as the spec of the TC wire, as long as its type-J wire it shouldn't be the problem. Check for any AC lines near your TC wire and make sure you don't have any junctions (or as few as possible) in your TC wire. When we run TC wire its always in its own metallic conduit to provide sheilding from any interfearance. In the case of the 205 I 've had to make sure the TC wire is always routed away from the power supply on the base, apparently ADC bases don't have much shielding.

Created Date: November 13,2002

Created by: Tech Guy

Showsys,

1) The THM module is a 16-bit resolution module, which consumes two words per channel, BUT the module converts the T/C signal into actual deg. C or deg. F with one implied decimal point. So according to the type of T/C you are using, you most likely will only be using values that are in the lower word. The upper word is mostly for diagnostics like a broken transmitter (burnout detection) and the negative sign bit.

2) For unstable readings you will most likely want to start by looking at the power supply being used for the THM card itself. With the T/C signal being a mV range it can be susceptible to noise, even a noisy power supply. Take the 0V that is connected to the F2-04THM and jump it over to the PLC's incoming power Ground. (even if you are pulling it from the base aux. 24 VDC) You want to make sure that you have a good solid earth connection and the PLC and module power supplies have a common reference.