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1216  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 26, 2010, 02:43:51 pm
http://s3.postimage.org/hcXiS-3a7c5d.jpg

Hopefully it has come through this time

jack
1217  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 26, 2010, 02:39:56 pm
Yes, you've got it now
here,s a slightly improved image of the circuit

You do appreciate that the controller has to have the mains supply powered up before the 4-20 circuit operates.

I suggest you leave the arduino disconnected until you have proven you get the correct voltage developed across the resistor.  (I note you called it a capacitor.

jack
1218  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 24, 2010, 03:50:40 am
Yep, there is indeed a wiring error.  You have connected the PSU negative lead to terminal 7 instead of the arduino ground.  This has placed the whole 12 volts across the 4-20 transducer without any burden resistor (220 ohms).  To iterate, terminal 6 goes to your PSU positive, terminal 7 has one end of the 220 ohm resistor connected and also goes to the arduino sense port.  The free end of the 220ohm connects to the PSU negative and also goes to the arduino ground connection.  

In all likelyhood therefore your controller 4-20 output is no longer working.  However it may have survived the trial by fire so it's worth having another go but this time correctly wred up.

I would also recommend that you disconnect both arduino connections until such time as you can confirm that you do indeed get a correct voltage developed across the 220 ohm resistor.  Once you have confirmed this then connect the arduino as the measuring device.

It is important when juggling wires like this that you draw out a circuit diagram showing where each and every wire goes before you power anything up.  This clarifies in your mind that what you are doing is workable.

With respect to  Wortelsoft's comment.  Provided the 220ohm burden resistor is ALWAYS connected as I have already emphasised then the arduino can accommodate a 4-20 circuit since the current is NOT flowing throw the arduino.  The arduino simply measures the voltage (which is limited to 4.8 volts) across the resistor.  If you wanted to be absolutely safe you could wire a 5.1 volt zener diode across the arduino input terminal and ground.  This would ensure that any wiring error places no more than 5.1 volts across the arduino.

Note that the arduino should be powered up before you energise the controller circuit since it is not a recommended practice to inject signals into unpowered systems.

jack
1219  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 24, 2010, 02:21:24 am
I take it you still had the 220 ohm resistor between terminal 7 and te arduino / psu ground

Even if the controller was already faulty, 12 volts can only drive 12/220 or 50 milliamps (approx) which equates to about 0.5 watts.  There is noway this could produce smoke.   It is probable therefore that you had a wiring error.

jack
1220  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 23, 2010, 02:46:38 pm
Have just had another look at your photograph and it seems to be wired up as I've suggested in the previous entry.  That being the case then it's possible that the 5 volt arduino supply is inadequate to excite the 4-20 transducer.   In industry we used around 28 volts volts to run 4-20ma current loops.  You could try attaching say 18 volts or so as the supply to terminal 6 rather than the arduino 5 volt source, with the 18 volt negative lead being commoned to the arduino ground.  However this exposes the arduino to a possible overvoltage if the 220 ohm resistor becomes inadvertantly disconnected so you might want to ensure it's very well connected.  

jack
1221  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 23, 2010, 12:52:52 pm
Not very good user guide but here we go again.

The 4-20 transducer within the controller can cope with a maximum supply voltage of 25volts (20ma x 500 ohms)
The instructions do not specify a minimum drive voltage but it should be capable of running off the arduino 5 volt supply.

Because the drive volts are coming from the arduino you need to wire as follows :

a) connect arduino 5 volt supply to the 4-20 + terminal (6) on the controller.

b) connect a wire from the 4-20 - terminal (7) on the controller to the arduino signal input.  You might want to insert a 1k resistor in this line to the arduino to limit input current under fault conditions but it's neither necessary nor, if used, will affect calibration.

c) connect the 220 ohm resistor from the  4-20 - terminal (7) to the arduino ground.

The system now operates as follows :

The controller 4-20 transducer acts as a variable resistor and controls the flow of current from the arduino 5 volt supply, through the 220 ohm resistor to the arduino ground.  This flow produces a voltage signal across the 220 ohm resistor which is your measured variable into the arduino.

4 ma will produce a 0.88 volt signal = 0%
20ma will produce a 4.40 volt signal = 100%

regards

jack
1222  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 23, 2010, 08:50:06 am
I see that it requires an external source to drive the 4-20 circuit.  Does any of the other 3 pages state what the minimum voltage is for this source.  The pages are legible so can you photogrqaph the other 3 so's we have all the information.

jack
1223  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 23, 2010, 08:18:16 am
I need to see the user manual before advising how to connect it up since you are obviously seeking exact instructions.  Can you either scan in the sheets or advise exactly what the markings are on each of the units user connected terminals.

jack
1224  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 23, 2010, 04:12:06 am
Firstly your device is not a sensor, it is a controller that needs mains power and suitable sensors connected.

It outputs both an analogue current (4 to 20ma) based on controller computation and a dry relay contact for use as an alarm or switching facility.

I cannot determine what it means by stating the relay is a 5volt unit unless it also outputs a 5 volt on/off signla for an external relay.  A copy of the operating manual should clarify this for you.

The device outputs 4 to 20 ma but can only do so if you present it with a load resistor.  I suggest you connect a 250ohm resistor between the terminals marked as 4-20 then connect the arduino input and ground across the resistor.  The 4-20 output will now produce a voltage signal of 1.0 to 5.0 volts across the resistor for the arduino to read.  Getting hold of a 250 ohm resistor might be problematic so use a 220 ohm and scale the arduino such that 0.88 volts equals 0% span and 4.40 volts equates to 100% span.

Jack
1225  Forum 2005-2010 (read only) / Interfacing / Re: Interpolation methods for predicting future on: November 16, 2010, 06:37:42 am
Don't wish to be picky, but prediction of future data is "extrapolation".  Interpolation is the assessment of data between two measured points.  ie it relates to history.
jack
1226  Forum 2005-2010 (read only) / Interfacing / Re: How to decrease voltage? on: November 14, 2010, 01:45:59 pm
By magic !  it's all done with smoke and mirrors.

A cars electrical system is a self contained system.  Battery output to device, out of device and back to battery.

Do not confuse the term "ground" with a stake driven into planet earth.  Thos devices are the preserve of vampires.
1227  Forum 2005-2010 (read only) / Interfacing / Re: Arduino with zener diode on: November 14, 2010, 01:36:07 pm
On the basis that the arduino can output only 40ma without going into self destruct the maximum zener required power rating is
5 x 0.04 = 200mW.   That's based on using a 5 volt zener  feeding into a dead short with 100% duty cycle of the PWM.  To protect the arduino one should fit a resistor in the output of the zener to limit current to 40ma.  The maximum resistor required is 5 / 0.04 = 120ohm. Again this is based on 100% duty cycle feeding a dead short but this time with the zener voltage set to zero volts
jack
1228  Forum 2005-2010 (read only) / Interfacing / Re: Arduino with zener diode on: November 13, 2010, 02:17:33 pm
Here's a simple circuit using a zener  (click on the image to see it)


The PWM output is a 5 volt signal of varying duty cycle (mark to space ratio).   The zener diode subtracts its voltage rating from the 5 volt output to produce a reduced output.  For example, if the zener is rated at 2.1volts the output will be 2.9 volts.

jack
1229  Forum 2005-2010 (read only) / Interfacing / Re: +-10V Analog input on: October 20, 2010, 04:36:55 pm
Apollo
Please tell us what language you are using and what software translator you are using to create the english translation.  If you send your last message, about curtain rods, in your original language we may be able to try a different translator.
jack
1230  Forum 2005-2010 (read only) / Interfacing / Re: +-10V Analog input on: October 17, 2010, 03:43:05 am
A simple voltage divider using a pair of resistors, say 2 resistors in series each of 3k3ohms  (that's 3300).  One end of the chain to your 10 volt output, the other end to the arduino 0volts and the centre to the arduino analogue input.  You also need to connect your cnc 0volts to the arduino 0volts
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