Current

Hay

I am controlling the gases using the solenoid valves, for interlock purpose I need feed back form the solenoid valve wither it is ON or it is in fail condition.
For feed back purpose I am planning to measure the solenoid current & convert current in to the voltage & give to the LPC2114 ADC input
Please provide the circuit for measurement of current and how to interface to the LPC2114 ADC input.

Regards
chandu

Solenoid monitoring

Chandu,
here are a couple of solutions :

(1) using and IC: I think you can use a device like National Semiconductor LMD18400 (**broken link removed**) that has a digital error flag to identify open or shorted load. It's indeed an high side driver, a feature always preferred in industrial applications.

(2) Using discrete driver: if you don't want to use an integrated device, you can use a low value resistor put between driver emitter and ground (assuming low-side driving, here). As an example, if the solenoid needs 400mA, you want to use a 1Ω resistor (½W). Now connect the emitter/resistor node to an ADC input of the microcontroller. This will give you 0.4V when the solenoid is working. If the microcontroller uses a 10-bit ADC converter for a 0-5 V range, you will have a 0x00-0x51 ADC range for the solenoid current. If you need an extended measure range, use an op-amp with a gain of 2 or 3 between the node and the ADC input. Every voltage is referenced to ground.

Basically just just need to wire a small value resistor in the solenoid circuit. You can then measure the voltage drop across that resistor with your A/D. If the solenoid is energized there will be some amount of voltage developed across the resistor (use ohms law to calculate the expected value). If the solenoid is de-energized then there will be zero voltage across the resistor.

Good luck

Lefty

Are these DC valves if so what voltage are they driven by ?