I need to record DC current load using a PC. Can someone give me an idea where to get started. I need information on parts that are proven. Need a dc motor that moves about 60 rpm and need to measure motor or current load on a PC

 

Well there are a few things that need to be considered . Do you have a common negative / gnd for the motor and electronics ? If so a simple shunt resistor will provide a voltage proportional to the current . Quickest a/d that pops to mind would be a PIC16F877 and send the data to the PC via RS232 , that would give you up to 8, 10 bit channels . It would be a good idea to put a resistor in series and with the input and clamp the lines incase of shunt failure . If you have to float the ground , you can still do that but will need to isolate your data lines ( opto isolator on RX and TX lines , seperate supply etc. for Max232 chip ) . Your serial format can be whatever you choose , personally I'm running Modbus on one of these on my bench already ( data logging some prototype instruments ) . All you would need to impliment is command 4 ( read 3x range ) and just map 16 bytes of RAM onto addresses 0000 to 000f .
You might want to look at the PWM output on that chip too , if you want to add PC control to the motors , need commands 3 and 6 for that though ( 4x registers read and write ).
If you want off the shelf equipment , and do have that common ground . Any PLC ( Control Micro , Modicon , Allen Bradley etc. ) will do fine , but will be a bit more expensive .

 

Using a standard 0 to 100mV DC shunt and a current converter you can convert Dc current to
4-20mA National instruments corporation should be able to supply you with a 4-20mA card for your PC.
Flexcore corporation has the Dc shunts and the Model SCE current converter. Hope this helps.

 

well, even i'm working on the thing you specified. what i've thought is to include a resistor in the drive circuit, so that it can hold the voltage and pick up that voltage across the resistor and give as input to adc0804 and then acquire the converted digital output from the parallel port.
If you can get something more or efficient let me know.
email: [email protected]

 

You are looking for either a current shunt or a hall effect device and an analog card for the PC. An alternative is an ammeter that has a serial or IEEE 488 interface. Typically, if the setup is right for the current shunt, it will be the cheapest. The current shunt usually has to be on the low side to stay in the common mode range of the card inputs. A hall effect sensor has isolation being magnetically coupled, but they are more expensive. As they have an amplified output, the analog card can sometimes be cheaper. While an actual ammeter with an interface used to be prohibitive, I've seen some very low cost instruments lately, so this may no longer be true. I've seen a complete DMM with 232 for less than $100.00 making this a viable option if you don't need to capture waveforms. A lot depends on your sampling rate.

Regards

cww