Instron Model 1000 help 2

[elopez]

Hi,

I am new here and am looking for some help with a tensile tester my company recently purchased on ebay. I am having trouble calibrating the machine according to the product manual. The machine is an Instron Model 1000. According to Instron, this specific test frame stopped production in 1987, so it is a bit difficult finding resources for troubleshooting/maintenance.

Firstly, the LVDT core assembly was damaged upon purchase, but we were able to source a replacement. During the steps of calibration, I am required to find a null value by adjusting the LVDT core assembly. However, when adjusting the assembly, it does not affect the load reading whatsoever. I am really at a loss here and in need of some guidance to some possible solutions.

Thanks for any help provided.

 

[TugboatEng]

LVDT is a position sensor and is not part of the load measurement.

 

[elopez]

@TugboatEng Correct. In the calibration procedures, it says to adjust the LVDT core assembly until a null value is found. The null value cannot be found when adjusting the assembly.

 

[3DDave]

The null for an LVDT is when the core is centered longitudinally in the housing.

When you say you cannot find it, how are you going about detecting this and what is the indication you aren't there?

 

[EdStainless]

the null value is when each end measures the same.
It is the magnetic center not necessarily the physical center.
And one reason that I went to strain gauge extensometers in place of LVDT.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[btrueblood]

Agree with Ed, there are a lot of better methods for measuring displacement than LVDT's.

 

[elopez]

@3DDave So the steps I am following are:
1. Set readout mode switch to TRACK position
2. Set range switch to 1/5 position
3. Hold zero switch in the ZERO position and use the coarse and fine adjustment knobs until LOAD readout shows zero
4. Release the zero/cal switch and change the RANGE switch to 10/50 position. LOAD readout is not indicating how well the core of the LVDT in the load transducer is nulled in its coil contained in the crosshead. This value should be less than 5% of the full scale of the load RANGE for the load transducer installed.

I am using a 1000 lb transducer (1262lb max capacity). When I reach the step above, the load readout is at 1325lb. The manual then says "If the load readout is greater than the value shown in the table above, use the screwdriver provided to adjust the LVDT core extender shaft in the crosshead until a null occurs. Rotate the adjustment CW and CCW to locate the null". This is the part I am asking about, when I adjust the extender shaft, the load reading remains static at 1325lb. Hopefully this helps. I can provide pictures if I am not being clear enough.

 

[btrueblood]

LVDT reading is what you should be trying to null, it has nothing to do with the load (force) reading.

 

[elopez]

Is there another way to do it then? I am just going by the manual instructions and it specifically states the load reading as the way to tell if the core is in a null position.

 

[btrueblood]

Your LVDT may be damaged enough to make it impossible to null by the manufacturer's instructions.

I'd look at finding new control software and instrumentation. These guys might be able to help you:

https://frankbacon.com/product/1k-5-kn-instron-1011/

 

[elopez]

Thank you for the resource. The LVDT core assembly is brand new. The LVDT coil on the other hand seems to be the one installed on the unit by the OEM. Unsure if its possible to change that out. I have been in contact with a reconditioning company, but my bosses want the cheapest solution possible.

 

[elopez]

In case anyone cares.

I was able to calibrate the machine after adjusting the height of the LVDT coil such that adjusting the core assembly actually registered changes in the load reading. Followed procedures outlined in the manual and it worked as intended. Thanks to all for the input and time.