Anderson level sensor cal to a control logix

I'm not a CLX guy, but I suspect that you need to calculate what 20mA represents and plug it into the CLX. But you haven't provided information on what range your Anderson sensor is spanned for.

Unless you can re-range the Anderson so 506"w.c. = 20mA, you'll have to live with whatever it is ranged for at full scale and use a calculated value for what 20.0mA equals in gallons or head.

As an example, suppose the Anderson is ranged 0-600" w.c. (and whatever's in the tank is a specific gravity of 1.000).
The 506" level at 25,000 gallons is 84.33% of span 506/600).

The corresponding analog value for 84.33% of span is 17.49 mA [(0.8433 * 16) + 4].

You need to make the 20.0mA value equal to some value so that 17.40mA = 506"w.c. What is 20.0mA equivalent to?

506/17.46 = X/20.0
17.46x = 506*20.0
x = 579.6" at 20.0mA

The same applies for units in gallons:
25,000/17.46 = X/20.0
17.46x = 20,000*20
x = 28,637 gallons at 20.0mA

Substitute your Anderson 20ma span value range and do the calcs. Then enter the value for what 20mA represents, and the levels are likely to come out OK.

What leads your production guys to think the cal is off? When I worked at a bottler we used to take monthly checks of silo sensors by pumping a known quantity into an empty silo (you may not have that option).

There is an offset value setting in ControLogix analog cards that you may look into as well--if that pertains to your unit.

The sensor's full operating range is 415.1 to 830"wc. We totalize the flow going into the silo, but if the cream density changes just a little then all the calculations are off, even the silo readings are off.

Page 22 of the Anderson instruction manual(http://www.andinst.com/PDFs/2008.pdf) explains how to calculate the Cur Cal value. The 415.1" to 830" is not the operating range, even though that is what the manual calls it. Those figures represent the minimum and maximum span for the instrument. So the transmitter can be calibrated anywhere between 0-415.1" and 0-830".

As you know, density changes in the tank will affect the level readings. You will need the density of the material to use in the calculation of the Cur Cal value. The Cur Cal value is used to set the span of the transmitter without having to apply the actual span pressure.

The value you use for the high signal for the analog input module will depend on the transmitter span and how you display the level value and/or how you use this level in logic calculations. For example if the transmitter is ranged 0-506" and that represents 0-25,000 gal, then the high signal would be set to 20mA and the high engineering units would be set to 25,000. Usually the high signal is set to 20mA and the engineering units are set for whatever 20mA represents. I've never tried it, but I believe the analog module does a linear calculation using the high and low signal values. So a high signal value of 16mA and a high engineering units of 18,750 would still calculate to 25,000 at 20mA.

If the density changes frequently and you are expected to recalibrate the transmitter often, it might be easier to set the transmitter span a bit higher than required for the greatest material density you expect to encounter and do the actual level calculation in the PLC. That way you could change a density tag value rather than having to recalibrate the level transmitter.

go_bears said:

The sensor's full operating range is 415.1 to 830"wc.

Click to expand...

And what is your transmitter set to in that range?

go_bears said:

We totalize the flow going into the silo, but if the cream density changes just a little then all the calculations are off, even the silo readings are off.

Click to expand...

The Anderson is head pressure measurement technology. Head pressure is always referenced to a standard, water column pressure, which by definition has a specific gravity of 1.000.

Head pressure measurements are ALWAYS subject to a deviation error in direct proportion to density changes. So your measurement is guaranteed to be off as density changes, that's intrinsic to the technology.

Like Danny Michael says, you need an easily accessible density correction factor.