Hi, I need to get the information in a 4-20 mA PLC signal using pic, I guess I can use A/D converters available in PIC MCU but I need a suggestion on...
... Yes, there is a special conversion circuit - 250 Ohm resistor :-) Josef...
Snail Instruments
snail@...
May 1, 2006 9:53 am
21715
Hello, This email message is a notification to let you know that a file has been uploaded to the Files area of the jallist group. File : /Serkan...
jallist@yahoogroups.com
May 1, 2006 10:19 am
21716
... It's really difficult - try a 250 ohm resistor!! Your voltage range is actually 1 - 5 Volts corresponding to 4 - 20 mA. You can use the loss of voltage...
That indeed is a simple solution, but I guess the voltage drop over the resistor might be a problem. Maybe it's an idea to use the ADC with a voltage reference...
... No! You terminate the 4 - 20 mA current loop with a 250 ohm resistor. You measure the voltage across the terminating resistor. This voltage will be ...
... By coincidence I measured the input impedance of a AD-channel of a 12F675 last week. At 10 kHz the equivalent impedance was 100 kOhm. The impedance is...
... Measuring the voltage across the resistor is indeed the obvious thing to do, that's not what I wanted to change (there must be a voltage drop across the...
... A 4-20 mA current source should mention the maximum voltage it can deliver. 10V is quite common. But the OP must verify this, and more important: is it...
... The 18F2420/2520/4420/4520 datasheet recommends a maximum analog source impedance of 2,5 kohms. The 12F629/675 datasheet recommends a maximum analog source...
Hello, When I connect a lm75 to a 16f84 on adress 111 (with:lm75_read_fdt( 7, f2, db, tb ),I get -55 degrees on the display. on adress 000 it is working. What...
... Wouter is right (as usual :-). The PIC18C reference manual states a minimum Vrefh-Vrefl of 3,0 Volts if you want to use the full 10 bits resolution. A...
... The input impedance and the minimum source impedance have no relationship. The input impedance can be determined by the average current through load the...
... Ok, but if you use a device with a lower input impedance, shouldn't you also use a lower value series resistor (in order to retain the same accuracy)? Just...
Hi If your really bothered about the impedance of the ADC can't you jsut use an Op-AMP as a buffer - unity gain. That way you will have an high impeance and...
Do these current loops have any defined relationship to ground? The last time I worked on current loops they were attached to teletype machines and had more...
... You software guys should get familiar with the Ohm's law. At least :-) The input impedance of the A/D converter is parallel to 250Ohm resistor. It is three...
Snail Instruments
snail@...
May 2, 2006 7:20 am
21732
actually the current sources are just pressure transmitters operating on 24 V supply, the current values are output in 4-20 mA range. I am going to try...
Hi Raymond, you probably forgot your pullups on your scl and sda lines. use any value between 3.3K and 10k. I managed to read values from the end of a 25 meter...
... Resolution != accuracy if you are interested in the real value, it makes no sense to A/D more finely that the *accuracy*. The resolution is interesting...
Hi, normally all 4-20ma output type devices mentioned in its data sheet, what will be the maximum loop resistance it can handle. some types its less than or...
Hi all, Wouter, you're absolutely right. Take a multimeter, range 2V, 1999 "counts". Specs (taken from manufacturer) 2%+5mV: - You can measure from 0V to...
A 4 -20mA loop is normally powered by a 24V DC supply. The limitation is the total resistance which can be up to 1200 ohms, therefore your 250 ohm sense...
... 1200 (=24/0.02) is the maximum *total* resistance in the loop, including the driver, so it is not a very relevant figure (1200 load resistance would leave...
Hi there, About a week ago I asked something about how to drive a lot of leds. I got very good replys! thanx again. Now I'm just testing with a far less amount...
I don't know if its of any use, but in the "tips and tricks" booklet I received with my PicKIT1 programmer it details multiplexing LEDs using various PICs (for...
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