Phase shift in cabling?
in [Design]
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From: DigitalPlease on 11 Jun 2010 21:26 On Jun 5, 12:24 pm, "mook johnson" <m...(a)mook.net> wrote: > "DigitalPlease" <mrperfection...(a)gmail.com> wrote in message > > news:5aafaf2e-ad18-419b-8141-54734805c857(a)w3g2000vbd.googlegroups.com... > > > > > > > I'm working with linear hydraulic actuators which have multiple LVDTs > > (for the ram and main control valve) and I have a spec for allowed > > phase shift from primary to secondary for the transformers. > > > I'm trying to make sense of the Labview code I've been given for > > measuring this parameter and have found an unexplained hardcoded > > offset value related to this phase measurement. My analog skills are > > down so I feel like I'm missing something obvious. > > > The setup is: The excitation board is connected to the actuator via a > > ~25ft cable. Excitation is ~1900Hz at 5V. If I probe either near the > > excitation board or near the actuator, I get similar measurements for > > a couple of different parts that are in the 3-7 degrees range, well > > within the +- 10 degree spec. The problem is, the hardcoded offset is > > 5 degrees so some parts pass and some parts fail. > > > I assume the cabling can impart some sort of delay thanks to > > capacitance/inductance of the line and perhaps this is where the > > offset is coming from, but I'd like to understand if this is correct > > and how I can characterize this to calibrate my measurement. > > Could it be that there is some analog filtering before the A2D that causes a > 5 degree phase shift at 1.9Khz? I've pulled the part off the stand and hooked a function generator to the primary and am measuring with a fairly nice Tek. The numbers I was quoting earlier were for a single leg of the secondary. The current setup is using three probes, one on the primary, Va, and Vb. I then use the built in math function to generate Va-Vb and measure the phase relative to that. I get the secondary about 8 degrees leading unloaded or with a voltage divider of 5k/65k (its target application has this on the output) on each leg. Is this the appropriate way to measure phase shift or should I load the output in some way? Calls/emails to the mfg about how they are doing it haven't been returned yet.
From: JosephKK on 11 Jun 2010 22:46
On Fri, 11 Jun 2010 18:26:07 -0700 (PDT), DigitalPlease <mrperfectionest(a)gmail.com> wrote: >On Jun 5, 12:24 pm, "mook johnson" <m...(a)mook.net> wrote: >> "DigitalPlease" <mrperfection...(a)gmail.com> wrote in message >> >> news:5aafaf2e-ad18-419b-8141-54734805c857(a)w3g2000vbd.googlegroups.com... >> >> >> >> >> >> > I'm working with linear hydraulic actuators which have multiple LVDTs >> > (for the ram and main control valve) and I have a spec for allowed >> > phase shift from primary to secondary for the transformers. >> >> > I'm trying to make sense of the Labview code I've been given for >> > measuring this parameter and have found an unexplained hardcoded >> > offset value related to this phase measurement. My analog skills are >> > down so I feel like I'm missing something obvious. >> >> > The setup is: The excitation board is connected to the actuator via a >> > ~25ft cable. Excitation is ~1900Hz at 5V. If I probe either near the >> > excitation board or near the actuator, I get similar measurements for >> > a couple of different parts that are in the 3-7 degrees range, well >> > within the +- 10 degree spec. The problem is, the hardcoded offset is >> > 5 degrees so some parts pass and some parts fail. >> >> > I assume the cabling can impart some sort of delay thanks to >> > capacitance/inductance of the line and perhaps this is where the >> > offset is coming from, but I'd like to understand if this is correct >> > and how I can characterize this to calibrate my measurement. >> >> Could it be that there is some analog filtering before the A2D that causes a >> 5 degree phase shift at 1.9Khz? > >I've pulled the part off the stand and hooked a function generator to >the primary and am measuring with a fairly nice Tek. The numbers I >was quoting earlier were for a single leg of the secondary. The >current setup is using three probes, one on the primary, Va, and Vb. >I then use the built in math function to generate Va-Vb and measure >the phase relative to that. I get the secondary about 8 degrees >leading unloaded or with a voltage divider of 5k/65k (its target >application has this on the output) on each leg. > >Is this the appropriate way to measure phase shift or should I load >the output in some way? Calls/emails to the mfg about how they are >doing it haven't been returned yet. Set up a test jig as close to actual use as possible, measure at the same places as actual use. |