WetCoastWillie
New Member
Does the ELK M1 support a 4-20mA analog input, It looks as though the main board does not have said input but is there an expantion module available that would support such?
Thanks
Thanks
4 - 20mA input for the ELK M1
- Thread starter WetCoastWillie
- Start date
znelbok
Active Member
No, but it can be done. I have two 4-20ma inputs at the moment.
On an input expansion board you need to remove the pull up resistor (this make the input basically measure voltage only and not supply power).
Then use a suitable resistor for the 0-12v range (cant remember what size I used). Small caveat here - the input range is 0-13.4 volts when on AC supply and 12V when on battery.
I use a 24V power supply to power the 2 wire loop powered transmitters and measure the return current (4-20mA) with the aboe setup.
The M1 is a little coarse with only 256 steps from memory, but its better than nothing.
Mick
On an input expansion board you need to remove the pull up resistor (this make the input basically measure voltage only and not supply power).
Then use a suitable resistor for the 0-12v range (cant remember what size I used). Small caveat here - the input range is 0-13.4 volts when on AC supply and 12V when on battery.
I use a 24V power supply to power the 2 wire loop powered transmitters and measure the return current (4-20mA) with the aboe setup.
The M1 is a little coarse with only 256 steps from memory, but its better than nothing.
Mick
BraveSirRobbin
Moderator
You would need a computer or some type of software to convert the equation from an analog or bit value to engineering units (such as temperature) that would now have a "Y intercept", or offset instead of just a direct ratio.
The voltage range would depend on the resistor value chosen to convert the current to voltage (V = I * R) where I would be the 4mA and 20mA values.
You could also do this imperically is its easy to run the sensor through a few values that you could correlate to some sort of calibration measurement.
Reference this How-To on Analog to Digital Converters that I wrote a while ago.
The voltage range would depend on the resistor value chosen to convert the current to voltage (V = I * R) where I would be the 4mA and 20mA values.
You could also do this imperically is its easy to run the sensor through a few values that you could correlate to some sort of calibration measurement.
Reference this How-To on Analog to Digital Converters that I wrote a while ago.
znelbok
Active Member
Yes you need something that can scale the number from the Elk. I use CQC and scale it there.
The conversion is jus the equation for a straight line. (y=mx+B)
So if a 4-20mA temperature transmitter was used you would have
y = 6.25x - 25 (where x is mA, y is temp)
or
y = 10.42x - 25 (where x is V, y is temp)
As for the resistor value, you need a max of 12V so 12/.0.2 = 600 ohms is what is needed.
You will see 0V - that is what 4-20ma systems are for. 0V represents power failure/signal loss.
So with a 600 ohm resistor you will have a voltage range of 2.4V to 12V. Should you see 0V (or whatever 0V represents) you know you have a problem.
Mick
The conversion is jus the equation for a straight line. (y=mx+B)
So if a 4-20mA temperature transmitter was used you would have
y = 6.25x - 25 (where x is mA, y is temp)
or
y = 10.42x - 25 (where x is V, y is temp)
As for the resistor value, you need a max of 12V so 12/.0.2 = 600 ohms is what is needed.
You will see 0V - that is what 4-20ma systems are for. 0V represents power failure/signal loss.
So with a 600 ohm resistor you will have a voltage range of 2.4V to 12V. Should you see 0V (or whatever 0V represents) you know you have a problem.
Mick
Any guidance on exactly which pull-up resistor would need to be removed on the M1XIN? I am trying to make Z16 on the board read a -20 mA analog input from a level transmitter.znelbok said:
Also, is there no way to scale the signal in the Elk so that I can display the scaled valve on a Elk keypad? The thought of having to send the raw information to a separate computer just to do a little scaling math (and then send it back to the Elk so it can be displayed) is frustrating.
Thanks
