4 to 20 MA Source Circuit Diagram

Please give more detail. What are you trying to do? Are you transmitting a signal from a sensor? What is the output (voltage/current etc.)? A brief outline will help us find a suitable solution.

i need for 4 to 20 pneumatic valve popsitioner. as well as testing the pneumatic instruments for testing and operTIN PERPOSE IN FIELED AND LAB

VOLTAGE 24 DC AND CURRENT IN STEPS 4-8-12-16-20

thanks for all for help me.actulay i use this circuit for electropneumatic valve positioner calibration in field as well as in inst lab.i nee such circuit which operateing voltage from 9 v battery and gives linear current out put 4 to 20 ma or fix current out put like 4,8,12,16,20.

i need very simple circit which electronics component are available.

thanks agian for instresting and help me

jamsshed

What you can do is to change the 20k resistor into many calibrated values and switch then using a simple rotary switch to get desired current in steps. The circuit will be independent of the load resistance to with 50 ohms to 500 ohms which is good enough for most of the applications including one you have asked for.

If you want some one to design and give you then you much be ready to pay as all engineers are paid.

yes

The module I linked to in #26 will do this.

Try this circuit diagram. It will work if you do as shown in the picture below.

Dear Sir

Using 9v battery could be possible to operate the regulator(7805)

then cct could be used in the field.

if using the loop voltage,

1- disconnecting variable input.(pressure,flow,etc)

2-inserting variable resistance 250 ohm and that could be used as variable current source

regards

TARIQ Z. KHALIFA

Yes, 9V operation is possible. You can also use LM78L05 as this circuit hardly draws LED lighting current. LDO can be used if low battery voltage is desired. Remember and use the pin diagram for the regulator from catalogs as 78L05 has different pin diagram.

Deatr Sir's

I have some digtal circuit on web using some IC,s like LM324 and other for transmitting and reciving 4~20 ma.

please if you have like this circuit diagram please inform me

Thank you

Abdul Majeed

please send me

With regards,

Siva.

Dear sir,

Instead of using LM7805, I have used L7805 which is told by vendor and designed the circuits. I am getting 5.6m.A to 10.6m.A variation. Where am I wrong/ How to improve it.Please help me.

With regards,

Siva.

There should be no problem with the L7805 - it's essentially the same thing.

I suggest you check all your connections (solder joints, screw terminals, wiring etc) carefully.

Also, if you've using a variable resistor to control the output current, make sure it's a good one - not something reclaimed from an old instrument, or dragged out of someone's spares box (unless it's been tested and proved to be a good part). Try giving it a squirt of contact cleaning fluid, & turning briskly from minimum to maximum a few times. Bad wiper connections can often give spurious results.

Hi

What about the quiescent current (Iq) of LM7805? Whould this not flow from pin 2 and thus sum with controlled current? Isn't controlled range of this proposed circuit therefore: 5.23mA to 10mA (datasheet says Iq=5mA)? How does one negate this Iq value and get 4mA to 20mA range as required?

Hi Guest,

Good question.

Yes, Iq gets added with regulator output current. It is to be taken care in setting a dial for display of current.

Iout = Iq + 5V/R

Hi,

Very helpful this section. So I tried to use 78L05 because I need to operate with 9V and the range of current that I can get is from 2.67 ma up to 4.78 ma, I saw that to achive 4.00 ma when the regulator was on 3.6 K

Any help welcome

Thanks a LOT

Evan

If your Load resistance is high then use higher input voltage than 9V at input and perhaps two 9V batteries in series forming 18V will be much better. 9V is critically lowest voltage and perhaps may be OK for 50 ohms load resistance. For 100 ohms, use 12V input power source. For greater than 1K load resistance you need 30V source Voltage. Never try more than 1K load resistance as you may easily damage the regulator.

For very high resistance value very special design is required.

Thanks for your reply,I am trying to have a tool (4-20 ma source) to test indicators in control panels. (some of them are in the field). Most of them have 250 ohm input resistance.In some cases two of these indicators (level or flow) are connected in serial which is 500 ohms but I can split them.

The thing is that I tried in my lab with 12V and I had the same result, instead 4-20 ma something like 2.6 to 4.7 and to me looked like power supply was not an issue.

Thanks a lot
Evan Kosteroglou

500 ohms X 20mA makes 10.000V across resistance and regulator requires 9V for itself to work properly. Hence 20V power supply to be used for testing and perhaps 24V supply is OK which is easily available in industries.

Use 5K variable resistance with 250ohms in series to limit the maximum current to about 21mA-22mA which then minimum current will be about 2mA to 3mA. Now you can vary 5K resistance to get dynamic current you need. See my earlier diagram above to refer.

.

Thanks a Lot

hello,

I made this circit some years ago,workjng very well

I make PCB for this circuit and This pcb available from me to all amatures and hobyest

I m thanking for mr, shayam how provide this circuit to all,

i tritd this circuit to repair a positioner was coms with me for repair so complete the job so now I can say this schematic is working good,

also I need any devlopment from any friend is well come

A M Tahir

amtahir786@yahoo.com

Er, um, by reading the Lee Dickens catalogue (not an endorsement), perhaps?

all these circuits i tried use full .i m thankfull to all for help me.now i need another circuit if variation in out put ma means not stable out put such gas detector i just need such circuit that i minimize or damp or slow response of out put ma.

any body have that an idea

thanks

jami

Dear Jami

Use a 0.1uF capacitor in parallel with measurement resistor or meter. This will have damping effect on the signal. You can also use larger capacitor to make it very slow to respond. If you use electrolytic capacitor then watch out of polarity. polyester or mica capacitors are far better. you can also use ceramic disk capacitors but they may introduce some temperature noise if they are very small size.

Hi all Expert,

I need a circuit diagram that convert 0ohm - 100M ohm to 4 - 20mA or 1 - 5v, with the zero and span adjust. Means when the input signal is around 0-500ohm and I can adjust the zero point to 4mA or 1V. And the the input signal is around 100M, then I can adjust the span point to 20mA or 5V. Hope that I could get some help from you all, Thanks

For a 4-20mA version, you'll need some active electronics (i.e. an op amp + a few scaling resistors) - or a 2MV supply!

For 1-5V, I think you can do it with just resistors - but you'd have to have a very high input impedance for measuring the voltage.

What is the input impedance of your measuring circuit? What error can you tolerate (due to the loading of the measuring circuit)? What power supply rails do you have available?

More information, please!

The easiest way to make a adjustable current source is with an LM317 regulator IC it is avaliable in a TO-92 or TO-220 package depending the current range you need 1ma to 1.2A. The supply voltage is connected to the +input of the 317 and a 1K 2W potentiometer connected in series to the output of the 317 with the adjustment pin of the 317 connected to the other end of the Potentiometer (current output) lead when the pot is adjusted to short down to 1 ohm the output current will be 1.2A when the pot is adjusted to 1K the output current will be 1ma you can use fixed resistors to limit the adjustment range the formula for output current is:

1.25/R(Pot value)=Iout

1.25/Resistance of Pot= Current output

please prvide the cicuit details for LM317 as a 4~20 ma source

thank you

hi,

Can you please send me a circuit diagram for 4-20 ma source

thanks

Evan

my email is [email removed]

thanks

CR4 Admin - email address removed

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For 100M ohms, you need a very special circuit, and to have to sit down on table for few months with serious plan. Hotch Potch circuits will simply fail and your time will be wasted and only disappointments to come. Get ready for a tough plan and then you will fail many times but finally will make it.

Look for very high impedance circuits having 100fA bais current like AD549LH, OPA129U, LMC6001A etc. Also go through their application notes, specially those are from Bob Pease http://www.national.com/rap/ at National Semiconductor for low current measurement and LMC6001.

Good Luck.

One can buy 4-20mA sources from many electrical suppliers (not an endorsement).