Looking for CT to get response from 1700khz.   - Page 1
Forum section: electronics / testgear

author: viper
author_rank: Regular Contributor
timestamp: August 24, 2024, 05:20:44 am
content: Long story short, I dove into some irrigation repair work that I am familiar with, but this troubleshoot job took some skill. System is a 2-wire that uses digital over analog, with decoder modules placed in the field to tell valves to turn on.Main issue is, though job is complete, is even though I bought the CM2100B (love that meter!!!), and it has a VFC mode which as I recall is variable frequency mode, but no clue of the range, but I am very certain it could not see the current, or ignored it, on a solenoid that should be pulling about 40mA. I know the solenoid worked fine, I was just testing the meter.At some point, I need to be able to get some current data of the power going to a solenoid. It probably doesn't have to be accurate, and I am just fine using a CT and just reading a voltage response on that as a sign that current is moving.I think every OEM wants to hide their tech but I think the one I worked on runs about 1700hz, but I may stop in with a scope to see some stuff... I do know that control has a mode which flips the field to simulated 24VAC mode just so you can use a meter in the field. It works and my Fluke graphing DMM could then resolve that craptastic wave form. It was a choppy 30V and 62hz, but I could read it.So the goal is something cheap, I can clamp on a small wire without breaking connection, and get a response from about 40mA current. Usually things are either good or bad so it could damn near be a red light/green light type of deal. Problem is very few meters will show current on these digital systems.

author: ledtester
author_rank: Super Contributor
timestamp: August 24, 2024, 05:54:03 am
content: According to this post:https://www.eevblog.com/forum/testgear/vfc-on-a-multmeter/msg3006198/#msg3006198the VFC (sometimes called VFD) feature of a multimeter inserts a low pass filter on the input for a more accurate measurement of the voltage or current. So it might not be useful for measuring a 1700 Hz signal.Do you think the solenoid coil is driven by AC current or DC current? I would just use the normal AC current measurement function (or DC current function if you think it's DC) to measure the coil current.Or -- you could measure AC voltage (or DC voltage) across the coil because there will be a voltage drop when the coil is energized.Also, I doubt the current going through the coil is at 1700 Hz - that just doesn't sound right.

author: viper
author_rank: Regular Contributor
timestamp: August 24, 2024, 03:31:02 pm
content: Only thing I can say for sure at the moment is the solenoids are indeed 24VAC nominal, and run on traditional multi wire systems. What type of simulated sine is given to them is not known right now. I do know the controller has self diagnostic tools and will capture both the inrush and hold current of the solenoid. Couple that with the audible noise that the solenoid is working, and the valve is firing, there is certainly current.The CM2100 resolves down to 1mA, but would not even detect a whisper of current. Super odd. I probably would not care if the value was correct because usually these things either work or don't.