Sensor repeatability

[hringm]

Can anyone give a quick explanation or a link to an explanation of what sensor repeatibility would be measuring exactly?

I have two different sensors I'm using in a project, and for both sensors the repeatability is given as +/- 1 mm. Both sensors detect the presence of liquid when there is liquid present on the sensor. I searched around but couldn't find much explanation. I found a definition that said "Repeatability, as the name implies, refers to how often a sensor under the same input conditions will return the same value," which makes sense to me, but that doesn't explain to me why both sensors would have their repeatability given in mm.

Thank you in advance for your help.

 

[IRstuff]

mm would imply depth, thickness, distance. Knowing what the sensor is might help

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[hringm]

One of them is the Baumer LFFS Level Switch. The link to the page for the information is below.

http://www.baumer.com/product-news/...lffs-for-high-temperatures/d1bf328a6b/en.html

 

[MacGyverS2000]

I'm confused as to why your confused. If your substrate is at 85C with standard atmo, multiple readings will always come back with a readings that's within +/- 1mm of some nominal value. Change the temp, distance, etc. and whatever new set of measurements it gives will also all be within +/- 1mm of some nominal value. A week later, those same conditions will result in measurements within the same +/- 1mm bound seen previously. It may not be an accurate value, but it will be repeatable.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

Did you even bother to read the datasheet?

The Level Switch LFFS designed to detect levels in tanks, media separation and provide empty-pipe detection or dry-run protection for pumps.
A high frequency sweep signal is radiated from the sensor tip into the tank. The media will act as a virtual capacitor, which together with a coil in the sensor head, will form a circuit creating the switch point signal. This virtual capacity will depend of the di-electric value of the media.
By means of the FlexProgrammer 9701 the output can be configured
to either NPN, PNP or digital output signal. A damping of the output signal can be activated in case of a fl uctuating media level, e.g. during tank filling.

While it's not a completely syntactical English description, what part of that was unclear?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Viccuus]

I work with HRingm. Our question is not about the sensor specifically but about the nature of repeatability. Why is the repeatability measured in "mm"? If this sensor is for either the presence or absence of a liquid, why would repeatability be in "mm"? Are HRingm and I just over-thinking this and the "mm" refers to liquid level? That the liquid level required to trigger the sensor will be within +/- 1 mm? This is a bit aggravating since the sensor specs never tell us what liquid level is required to trigger the sensor, just the repeatability of it.

 

[IRstuff]

It measures the level using capacitance to determine layer thickness, therefore, it has a measurement repeatability in distance units. Otherwise, you would be buying a float with a microswitch.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Skogsgurra]

And that float/microswitch would also have a mm specification.

What is the question? And why?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[danw2]

These capacitance sensors can be so sensitive as to detect presence before the liquid contacts the probe itself. It depends on the medium (its dielectric) and geometry of the installation.

>Why is the repeatability measured in "mm"? If this sensor is for either the presence or absence of a liquid, why would repeatability be in "mm"?

Because the trip point depends on the sensitivity setting, the material, the and geometry of installation, none of which are predictable.

However, for the same material, sensitivity setting and geometry, the trip point will repeat within ±1mm. That might be 3 mm distance away from the probe tip, or having the probe tip immersed 4 mm, or some other 'distance', but for repeating conditions, the trip point is repeatable.

>Are HRingm and I just over-thinking this and the "mm" refers to liquid level?

Yes, but ±1mm with respect to the level it tripped before and before that, for repeatable service conditions. Change the service conditions and the level at which the trip point occurs varies.

>That the liquid level required to trigger the sensor will be within +/- 1 mm? Yes, within +/- 1 mm of wherever the sensitivity setting for that material and that installation produces a trip point.

>This is a bit aggravating since the sensor specs never tell us what liquid level is required to trigger the sensor, just the repeatability of it.

The manufacturer's crystal ball was foggy the day he shipped your unit and he couldn't tell what material you have or where you set the sensitivity or how you installed it. Maybe next time . . .