analog 1-5V

theripley

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Hi

I will using analog input of 1-5V from a pressure switch for monitoring purpose. I am using MITSUBISHI FX2N-2AD module for this purpose. But it is written on the manual the availabe denomination for analog input for this modelu are 0-10Vdc, 4-20mA & 0-5 V. (please see attachment)

Am I getting it right? There is written about offset & gain adjustment (but not programmble but rather physical)but i just can't seem to get.

"It is necessary to readjust the offset & gain value when FX2N-2AD is used in current input, 0-5Vdc or with an input characteristic the factory setting". What readjustment does it mean?

fx2n-2ad-0001.jpg
 
I'm thinking of using the factory default setting 0-10Vdc (0-4000)& just multiply the reading by 2 since I will only get 1-5Vdc from the sensor. But when I scaled 1-5vdc basing on scaled value of 0-4000, I get 400-2000 & not 0-2000. This would create a conflict on getting correct scaled value if I multiply by 2 since this will be compared to another analog value of 4-20mA (0-1000).

Please advice.
 
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by your description

0 volts will equal 0
1 volt will equal 400
2=800
3=1200
4=1600
5=2000
6=2400
7=2800
8=3200
9=3600
10=4000

So when you feed 1 to 5 volts you will still only be scaling across 400 to 2000
 
I am not familiar with the Mitsubishi PLCs, but I would imagine they have a Scaling Instruction.

If the Analog Input Card is a 4000 Count Card, I would have expected something like 800 for 1V, 2000 for 2.5V and 4000 for 5V if it is set up for 0-5V. I hope my math is correct, it is getting late.

Using 0-5VDC

Input Min = 800
Input Max = 4000
Output Min = 0
Output Max = Whatever you need.

If it doesn't have a Scale Instruction, you can do this with Math.

Stu.....
 
Gil47,

Yes, that's how I calculated it (well, basing on the 0-10Vdc factory default setting). It will create a conflict with the other analog signal with which it will be compared with since 0 is not equal to 400.

sthompson,

Yes, you are correct that by 1-5Vdc you can get 800-4000 scaled value if you base your computation on 0-5Vdc & not 0-10Vdc. I was thinking of getting it with math but the problem is the two analog values @ base 0Vdc or 4mA will have different values, i.e. 0 is not equal to 400. Well, I guess I can minus the 400 with 400 to get 0=0, but that will give me a headache because there will be exceeptions. I am seeing long arithmetic.

There is something written on the manual about offset & gain adjustment but it was not very condusive, it was not properly explained. Readjustment was mentioned but not thoroughly expalined how to adjust.
 
To scale a 1 to 5 volts against a 0 to 5 volts all you need to do is subtract 400 then multiply by 1.25.
or subtract 800 then multiply by 1.25.
Depending on which value is equal to the 1 volt value.
 
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Again I am not familiar with the Mitsubishi, but for the Analog Cards I have worked with. The Offset and Gain were for trimming the Calibration of the Channel. Not for resetting it for different inputs. That's not to see you couldn't do it, but there may not be enough range in the adjustments to do that.

As far as the Input goes, you could Scale it twice, once for display, and once appropriately for comparing to your other Input.

Stu....
 
To scale a 1 to 5 volts against a 0 to 5 volts all you need to do is subtract 400 then multiply by 1.25.
or subtract 800 then multiply by 1.25.
Depending on which value is equal to the 1 volt value.

Say:
At 1Vdc=400 (written to D10)
4mA=0 (written to D20)

\m8000\----------------[sub d10 k400 d100]
\m8000\----------------[mul d20 k2 d30] <just to = scaling>
\m8000\----------------[=d100 d30] (TRUE)

At 5Vdc=2000
20 mA=1000

\m8000\----------------[sub d10 k400 d100]
\m8000\-----------------[mul d20 k2 d30] <just to = scaling>
\m8000\-----------------[=d100 d30] (FALSE)

I would not get the same logic all the time.
 
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Again I am not familiar with the Mitsubishi, but for the Analog Cards I have worked with. The Offset and Gain were for trimming the Calibration of the Channel. Not for resetting it for different inputs. That's not to see you couldn't do it, but there may not be enough range in the adjustments to do that.

As far as the Input goes, you could Scale it twice, once for display, and once appropriately for comparing to your other Input.

Stu....

I understand, I appreciate your replies. Can you further elaborate the "scaling twice"? I have made a not so precise sample program on my previous reply. I think you are suggesting something I may not have considered.
 
You must already have a scaling block on your 4 to 20 mA, if the 4mA = 0 and the 20 mA = 1000

If you are wanting your answer across 0 to 1000, for 1 to 5 volts, or for that matter 0 to 20 mA.

Try subtract 400 then multiply your result by 0.625.
(This is the same as subtract 400 then multiply result by 1000 divided by 1600)

This makes a scaling block to change voltage or current readings to a percentage reading times 10

The pages you scanned are to small to be readable and I am not familiar with your Plc so I am only gaining info that you have typed to show how to do scaling
 
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Is the 4-20mA signal sourced from the card, or sunk back into it. do you have three terminals (+24V,IN+ & COM)? If so, to make the comparison easier, you can connect a 250 Ohm resistor from the 4-20mA return signal to the common. The Voltage generated across the resistor will be 1-5V (matching the other input from your pressure sensor). This would mean the scaling for both blocks would be the same.

Alternatively, if you had space in the cabinet, I'm sure you could use a converter from someone like pepprl+fuchs to change the 1-5V and 4-20mA signals both to 0-10V signals.
 
The pages you scanned are to small to be readable and I am not familiar with your Plc so I am only gaining info that you have typed to show how to do scaling

Im very sorry I will try to print out larger portion of the manual. Please see attachement.

2stepsforward,

The 4-20mA is coming from the analog output module (FX2N-4DA) which controls a regulator. The 1-5 Vdc from the pressure switch is the feedback from the regulating system that the regulation is correct (not over or under pressure). I will compare their reading so that I will know if the pressure is under or over, then an alarm system will be ON.

I have attached its wiring diagram, please see attachment III.

fx2n-2ad_I.jpg fx2n-2ad_II.jpg fx2n-2ad_III.jpg
 
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