I have a pressure transducer of this type: http://sensing.honeywell.com/product-page?pr_id=144494
The pressure transducer has current-output that ranges from 4-20 mA and pressure that ranges from 0-200 PSI. I want to use arduino to get pressure-values.
I connect the trandsucer to a 220 ohm resistor, and the other end to (v-) of the powersupply. Then i can use the analog input on the arduino and read the voltage, and calculate the current and the pressure.
I use a powersupply of this type: cotek ge-25-12 (i'm powering the arduino from the computer)
The problem is that the voltage before and after the resistor gets negative values (but the drop is positive), and the arduino can only read positive values from 0-5 volt.
Method 1 (connecting v- to arduino ground)
I tried to connect v- on the powersupply to arduino ground(i checked if i could do this by connecting a 10kohm resistor between v- and ground, and the drop was 0 volt) , in order to set it to zero. Then i could use the analog input on the resistor and read the voltage. I tried to measure the current with a multimeter while i increased the pressure using a air-compressor. At 0 PSI the current was 4 mA(like the datasheet), and when i increased the pressure, the current increased. But when i reached about 20 PSI, the current stopped increasing, and stayed at 5.47 mA.
Method 2 (not connecting v- to arduino ground)
Here the opposite happened, the current stayed still in the start (7.5 mA). But at 40 PSI, the current started increasing and gave correct results according to the datasheet.
Why does this happen? How can i solve this problem? Is it possible to get correct current values from 0-200 PSI? If i use method 2, is there any ways to read negative values?
The pressure transducer has current-output that ranges from 4-20 mA and pressure that ranges from 0-200 PSI. I want to use arduino to get pressure-values.
I connect the trandsucer to a 220 ohm resistor, and the other end to (v-) of the powersupply. Then i can use the analog input on the arduino and read the voltage, and calculate the current and the pressure.
I use a powersupply of this type: cotek ge-25-12 (i'm powering the arduino from the computer)
The problem is that the voltage before and after the resistor gets negative values (but the drop is positive), and the arduino can only read positive values from 0-5 volt.
Method 1 (connecting v- to arduino ground)
I tried to connect v- on the powersupply to arduino ground(i checked if i could do this by connecting a 10kohm resistor between v- and ground, and the drop was 0 volt) , in order to set it to zero. Then i could use the analog input on the resistor and read the voltage. I tried to measure the current with a multimeter while i increased the pressure using a air-compressor. At 0 PSI the current was 4 mA(like the datasheet), and when i increased the pressure, the current increased. But when i reached about 20 PSI, the current stopped increasing, and stayed at 5.47 mA.
Method 2 (not connecting v- to arduino ground)
Here the opposite happened, the current stayed still in the start (7.5 mA). But at 40 PSI, the current started increasing and gave correct results according to the datasheet.
Why does this happen? How can i solve this problem? Is it possible to get correct current values from 0-200 PSI? If i use method 2, is there any ways to read negative values?
