Logging voltmeter?

[zbang]

Looking for suggestions-
It looks like in the next few weeks, I'm going to have to track down some time-of-day related power quality and control issues. My trusty old Dranetz was finally put out to pasture a few months ago, so I'm looking for something new. It needs to be able to watch at least two separate voltage inputs, one AC and the other DC. Current would be nice, too, but doesn't have to run at the same time as the voltages. I plan to install and leave it for a few days and suck the data into a laptop, so it doesn't really even need a display. I'd also like to avoid spending $$$$ on it , and would rather buy than rent. Thanks.

 

[gar]

140904-1442 EDT

I have nothing specific to offer, but I have questions.

1. What is the AC voltage range? How high does this float off of earth ground?

2. Can an isolation transformer be used between the AC voltage and the measuring instrument?

3. What DC voltage range? How high does this float from earth ground?

4. Is a differential input amplifier required for the DC voltage measurement?

5. Can Hall sensors be used for current measurement?

6. The most important question is what is the required time sampling rate?

7. What is or are the purposes of the test? What kind of problem are you looking to detect?

.

 

[zbang]

1. What is the AC voltage range? How high does this float off of earth ground?
2. Can an isolation transformer be used between the AC voltage and the measuring instrument?
3. What DC voltage range? How high does this float from earth ground?
4. Is a differential input amplifier required for the DC voltage measurement?
5. Can Hall sensors be used for current measurement?
6. The most important question is what is the required time sampling rate?
7. What is or are the purposes of the test? What kind of problem are you looking to detect?

both 120 and 60 nominal (ungrounded)
yes
24v, also ungrounded
shouldn't be
sure, anything that works
a second is close enough

I can't go into too much detail, but the question revolves around whether AC sags are affecting the DC voltage, and whether a lowered DC line no longer controls some other components. Or it might be that the DC system is sagging on it's own and affecting the controls. Basically, I want to let something log the affected voltages so I can look for correlation. Current monitoring is for future use; if I'm getting a logger, it would be nice to have current in addition to voltage.

In the end, I might have to set up a digital 'scope with multiple probes and some level-based triggers, but that would require borrowing it from another group and reading the manual.

 

[gar]

140804-1705 EDT

zbang:

For the DC voltage measurement you will need a differential input amplifier or an isolated DC input to output coupler. There are operational amplifiers with DC isolation. An isolated A to D converter can be used for the DC measurement. A small filament transformer with a diode bridge and a small filter capacitor can provide a DC signal from the AC supply voltage.

A DC data acquisition system can then monitor these signals. DATAQ is one company. Another is http://www.mccdaq.com/PDFs/specs/USB-200-Series-data.pdf . Two single ended inputs could have the digital outputs combined to produce a differential measurement.

You can search the internet for various sources.

.

 

[gar]

140906-2200

zbang:

The following is an isolated amplifier for voltage or current sensing. But requires an isolated +5 VDC power supply on the input side. http://www.avagotech.com/docs/AV02-2460EN

If on the DC side one of the power supply lines did not exceed about 40 V relative to common of your instrumentation, then this amplifier might work http://cds.linear.com/docs/en/application-note/an105fa.pdf .

The following amplifier includes an internal isxolated power supply for the input side http://www.ti.com/lit/ds/sbos001/sbos001.pdf . Good for 1500 V RMS isolation, tested at 5600 V.

.

 

[junkhound]

If you have a cheap laptop you can leave on site, take a look at picotech.

Software used to be open source, all the data logger is a connector and a $5 chip if you want to make your own additional units.

Or, get a used 1st gen scopemeter like Fluke 123 with the FO ouput to laptop, have seen them go for under $200 on ebay.

 

[zbang]

If you have a cheap laptop you can leave on site, take a look at picotech.
Or, get a used 1st gen scopemeter like Fluke 123 with the FO ouput to laptop, have seen them go for under $200 on ebay.

Picotech :slaphead:, and I even subscribe to nuts-n-volts. On the one hand, I'm trying to avoid building anything, even signal conditioning, OTOH, I'm cheap. Will check ebay, too.