Dear all

I have an Analogue input module which channel NO.3 has been set to 0-20mA, whilst my transmitter give 4-20mA. How can I do a correct scale? please give an example and write the equation for more information.

Thanks a lot

MJ90

Dear all

I have an Analogue input module which channel NO.3 has been set to 0-20mA, whilst my transmitter give 4-20mA. How can I do a correct scale? please give an example and write the equation for more information.

Thanks a lot

How and for which analog measurements can you use the function FC105 "SCALE" to convert the integer values (INT) into real number values?

How can you standardize and destandardize analog values with STEP 7 V5.5?

Thanks sir. that's a normal condition.

my condition is a bit different. my adjustment is 0-20mA but I have4-20mA.

according to the AI if I send 4mA to AI the A/D convert it to 5529.6, but 4mA is equal to 0.

how can I solve this problem? 

Hello,

it's time to tell us finally what exactly HW you're use, complete order number of AI module and how you connect your sensor to module. 

Duris_I

Hello,

it's time to tell us finally what exactly HW you're use, complete order number of AI module and how you connect your sensor to module. 

 Hi sir

 I used the AI with the order number 6ES7-335-7HG02-QAB0. the channel NO.3 has been set to 0-20mA, and I have connected a transmitter which produce 4-20mA to it.

Hello,

ok and what value you have in case of +/- 20mA? Pls check/measure for real not say from table. It's strange if you have set measure range to 0-20mA and sensor with 4mA gives you 0, I expect not correct cfg of module (other as you expected) or sensor problem. I recommend documentation for sure, there are so much possibilities of cfg and diagnostic: SM335 Analog module Manual

Duris_I

Hello,

ok and what value you have in case of +/- 20mA? Pls check/measure for real not say from table. It's strange if you have set measure range to 0-20mA and sensor with 4mA gives you 0, I expect not correct cfg of module (other as you expected) or sensor problem. I recommend documentation for sure, there are so much possibilities of cfg and diagnostic: SM335 Analog module Manual

 I don't want to make any change to cfg.

I wanna change the programm only. I'm not allowed to change cfg.

Please help me to solve my problem via programming.

MJ90

I don't want to make any change to cfg.

I wanna change the programm only. I'm not allowed to change cfg.

Please help me to solve my problem via programming.

Hello.

The instrument you use gives values between 4mA and 20mA.
The PLC card measures between 0mA and 20mA.

The scaling is done as if measuring between 0mA and 20mA..
even if not using between 0mA and 4mA.

The image above assumes you have 0 units
(whichever engineering units you are using).

The maximum measurement the instrument gives at 20mA is X units.
The minimum is at 4mA is assumed at 0 units.
The projected (fake) measured value at 0mA is predicted at Y units.

With this information, go back to the 1st link I supplied in my first reply. Read the 2nd example in the official FAQ.

Using FC105 you will have X as high limit and Y as low limit.

You will need to say what your instrument measurements are at 4mA and 20mA, if you require numerical values for X and Y.

 Somebody invited me to answer this question to my official mail id ([snip]). Anyway, I will share some my knowledge  too.

MJ90

Please help me to solve my problem via programming.

I will give one equation which you can use to convert RAW value to Engineering value or vice versa . I used it in one my project with  simatic manager.

1) Please make the calculation with pen and paper.

2) Find the RAW value for alarm.

3) Use Comparator block(CMP) to set alarm / bit high if value exceed the set point. 

mA=(Sensor RAW value * 0.000579) + 3.9995

So RAW value= (mA-3.9995)/0.000579

Example1:

If you want to rise an alarm on 20mA then

corresponding RAW value=(20-3.9995)/0.000579=27634

Use CMP block to set bit if the Value from sensor(Analog input INT) is greater than 27634.

Example2:

Similarly, If you want to rise an alarm on 0mA then

corresponding RAW value=(0-3.9995)/0.000579= - 6899

Use CMP block to set bit if the Value from sensor(Analog input INT) is greater than -6899.

Attachment: Attachment program made in TIA Portal V15.1 , S71500 PLC.

Yours is S7300 and simatic manager .So use comparator method.

My Advice: I recommend to check HW  properties to change mA setting Config,

because some of the sensors, mA between 2mA -4mA Means sensor Fault;  1mA-2mA Means Sensor Calibration Mode;  0mA means Power loss.

The above parameters needed for programming and alarm generation.

How do you distinguish sensor power failure  and actual reading 0mA?                                                                   

Note:

You can set High and low mA values in SCALE block. Attachment contain 4-20mA  settings.