Encoder to 4-20 mA

Hello All,

I have a PLC with analog input and output modules (4 - 20mA). i like to make a demo to practice PID control. It is a DC motor speed control demo (small DC motor). My DC motor has a Encoder with 150 pules per round ouput. So, how can i change this pulse output to 4-20 mA ?,so that i can feed 4-20ma signal into PLC input module as feedback.

Could you please help me where i can find the diagram circuit of this ? i'd to make it by myself, for cheap.

Thanks

Don't try

Small motors are actually much harder to control than big motors because they have much faster response than what PLC can possibly provide. Second, PLC PIDs are not setup to control motors well.

Try looking at the Excel spreadsheets in the PID threads.

To answer your initial question, REd Lion, M-Systems, and many others have signal conditioners that will convert the pulse to a 4-20 mA signal. You have to make sure that your encoder pulse frequency, voltage, and signal type (NPN PNP or whatever) are compatible. I suggest you have the encoder specs and wiring diagrams ready, and get application assistance from a local supplier for one of these companies.

I have worked with devices like that Tom is reffering to, and man what a life saver. In the "Frequency to Analog" converter as I believe they are reffered to as in this case, you have variable settings to establish the incoming frequency in relation to the 4 - 20 mA signal. The ones I used were performing a scaling function of x counts per second = y mA. Extremely handy units to use, I had actually used them in a direct loop with AB Powerflex drive for flow, and worked great, response time was variable in the setup software for the scaling values, which allowed me an error of 0.01% on a 450 g/sec flow rate, which was awesome considering how simple the circuit was.