Salt Dilution Uncertainty and Proposed Metadata Requirements CWRA Conference Vancouver Gabe Sentlinger Mar 7, 2013

AR s Salt Dilution Uncertainty and

Proposed Metadata Requirements

CWRA Conference VancouverGabe Sentlinger

Mar 7, 2013

AR s Quantifying Uncertainty (Content AZ, Photo GS)

Don’t torpedo your measurement!-We all have different methods for SD, we want to identify sources of error/uncertainty and control for them. -Ensure calibration, repeatability, linearity of method

Use standard error propagation relation

In most cases δM is small (0.1 %) can be in the range of 1-10 %δCF.T is based on calibration procedure and site specific regression if no calibration was done (2-7 %)

TCFdtbgECtEc

MassQ

.)()(

TCF

TCF

dt

dt

bgECtEC

bgECtEC

M

M

Q

Q

.

.

)()(

)()(

)()( bgECtEC

AR s Possible RISC Standards: Error Budget

• So maybe we have an Error Budget that we need to work within for a given RISC Class. Where do we want to spend that budget, where is the low-hanging fruit?

Class A 7% Class B 15% Class C 30%

Glass 1% Plastic 2% none

CF.T in field 1% site specific CF.T 5% constant CF.T 10%

pre-weighed bagged salt 1% off the shelf salt 3% "bunch of" 20%

two probes (US-DS or LB,Thal) <30% one probe ? "tasts salty" ?

several measurements s/2 one measurement s no measurements

dosing >1kg/cms var dosing <1kg/cms var

sensor accuracy 0.05% FS 0.05% sensor accuracy 1uS/cm <5%

baseline, averaging, sloped var constant baseline varstandard using streamwater var standard using distilled water var

AR s Lowest Fruit: Mixing Error

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1/13/13 10:12 1/13/13 10:13 1/13/13 10:14 1/13/13 10:16 1/13/13 10:17 1/13/13 10:19 1/13/13 10:20 1/13/13 10:22

Date:Time

De

lta

[N

aC

l] m

g/m

l

Left Bank

Thalweg

Right Bank

• Currently unquantified. Multiple probes, or injections, can help determine appropriate mixing reach for given Q

• This is a single pulse measured on left and right bank, and thalweg. Standard Deviation ±21%.

Left Bank Q = 0.245 cmsThalweg Q = 0.297 cmsRight Bank Q = 0.345 cmsAverage Q = 0.304 cmsSwoffer Q = 0.297 cms

AR s Impetus for Study: Automated Gauging

– How much error is introduced by assuming a CF.T for automated measurements?

– Is CF.T a function of EC.T? It shouldn’t be.– Is CF.T a function of Instrument? It shouldn’t be.– Is Background EC.T constant over measurement?

AR s Constant CF.T or Site Specific?

• This histogram shows that 95% of CF.T values are within 5% of the median value. So if you just used the median CF.T value, only 5% error introduced into Q measurement.

• Recent improvements to methods may eliminate the site specificity.

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%Median of Site

%T

ime

%

95% of values within median CF.T value of site.

AR s Need for fast, accurate, reproducible method

– Reduce the amount of salt required for a given flow/ reduce uncertainty associated with salt dilution measurement.

– Establish SOP to ensure data quality and traceability, quantify uncertainty, and protect sensitive habitat.

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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Salt Injection Concentration (kg/cms)

%U

nce

rtai

nty

in Q

(al

ph

a =

0.0

5)

Inst.Err:0.01 uS/cm and Trans.Time: 10 mins






Inst.Err:1 uS/cm and Trans.Time: 10 mins



AQUARIUS RESEARCH & DEVELOPMENT INC.

AUTOSALT

Jun 11, 2012

Uncertainty as a function of Instrument Accuracy and Transit Time

Notes:1) This plot shows the relationship between instrument error and required salt slug injection concentration.2) The "Inst.Err." value is the uncertainty in the measurement, which is a function of the signal stability, the instrument resolution, and instrument accuracy.3) The current acceptable range of uncertainty and Injection concentration excludes instrument error of 1 uS/cm and transit time greater than 10 mins.4) The target range is primarily from an Instrument Error of 0.01 uS/cm. This resolution is not available on most commercial sensors when the baseline conductivity is greater than 20 uS/cm.5) Assumes complete mixing, stable background conductivity, and insignificant error from Concentration Factor and Salt Mass measurement. Uncertainty in background conductivity included.

Acceptable Range

Target Range

D:\users\gsentlin\AQUARIUS_R&D\BUSINESS\Research&Development\AutoSalt\Data\Instrument\[Raffuse_SD-CM_Apr 13 2012_InstrumentNoiseModel_v0.2.xls]Notes

AR s Instrument Accuracy/Resolution

– What is the limit of the instrument?– This is a Unidata 6536B with resolution of 0.01 uS/cm but

accuracy of 0.5% of the reading. We found quanta of 0.3uS/cm.

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04/13/201213:26

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04/13/201214:24

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04/13/201215:36

Elapsed Time (s)

EC

.T@

25oC

(u

S/c

m)

EC

(u

S/c

m)

CCTBackground C (uS/cm/oC)Background CT (uS/cm)Alt_BaselineALT CT

1.3 kg/cms3.01 cms ± 11%

0.69 kg/cms3.68 cms ± 11% 0.29 kg/cms

3.52 ± 16%0.17 kg/cms3.07 ± 104%

Unidata 6536BRes: 0.01 uS/cmAccuracy: 0.5%

step = 0.3uS/cm = 0.7% = ± 0.35%

AR s Instrument Accuracy/Resolution

– Oakton Con110 has better accuracy and resolution at lower ranges, higher SNR, therefore less uncertainty in Q.

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100

04/13/201213:26

04/13/201213:40

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04/13/201214:09

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04/13/201214:38

04/13/201214:52

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04/13/201215:21

04/13/201215:36

Elapsed Time (s)

EC

.T@

25oC

(u

S/c

m)

EC

(u

S/c

m)

CCTBackground C (uS/cm/oC)Background CT (uS/cm)Alt_BaselineALT CT

1.33 kg/cms3.03 cms ± 4%

0.69 kg/cms2.90 cms ± 6%

0.29 kg/cms2.88 ± 6%

0.16 kg/cms2.96 ± 13%

Oakton CON110AutoRangingRes: 0.05% FullScale Accuracy: 1% FS + 1 digit0-20 uS/cm: 0.01 uS/cm, ±0.2 uS/cm20-200uS/cm: 0.1 uS/cm, ±2 uS/cm

step = 0.1 uS/cm

AR s Calibration Party!

-Salter kitchen scale 5000±1 g ml: $35. -MyWeigh BCS-80 scale 80±0.02kg: $171.-JScale HP-50x 50±.01g: $29.

Scale Typical Mass Resolution %Error

50g 1 0.01 1.0%

5000g 2000 1 0.050%80kg 20 0.02 0.10%


-10 ml graduated plastic syringe stated error ±0.01 ml, free(!) at pharmacy.-102 ml ± 0.069 ml, which is 1.4%.- I use 5.02 ± 0.048 ml, or 1.0%.-No significant temperature effect over range of interest (0-25ºC)


-1000 μl pipettor Diamond Pro : 275$-measured 997 ± 5ul (0.5%)-did not measure temperature dependence


-5 ml glass pipette stated error ±0.01 ml, with bulb 15$.-41 measurements, average volume 4.99 +/-0.035 ml (0.7%).

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Temp (oC)

Mas

s (g

)

Measured Mass

Calculated Mass

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1001

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Temp (oC)

Den

sity

(g

/l)

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-0.20%

-0.10%

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0.10%

%E

rro

r fr

om

1kg

/l


-1000 ml plastic graduated cylinder stated error ±10ml at 20ºC: 64$-20 measurements, average volume 500.5 +/-2.1 ml (0.4%). -temperature dependence of 0.1 ml/ºC, 1ml in range from 0-10ºC, less than

measurement error.


-500 ml glass volumetric flask ±0.2ml at 20ºC: 35$-not calibrated, assumed to be within specs. -Total cost of calibration party, 22$, reduction of total error by approximate 5%.

AR s Need for fast, accurate, reproducible method

– Uncertainty should be a trade off between effort/cost and accuracy. – For example, lab glassware is more accurate, but more expensive, fragile, and

difficult to use in the field.– Plasticware is less expensive, more rugged, but less accurate and subject to

temperature effects. But to what degree, should we worry about it?– Our tests show that there is a temperature effect of 0.1 ml/oC.

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Temp (oC)

Gla

ss V

olu

me

(ml)

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1.0%

%E

rro

r

Range of interest: ±1.7ml or 0.3%

AR s Calibration Factor Error (in progress)

• We’ve (AZ) identified a problem with a pre-mixed standard solution of salt and distilled water. The distilled water in the standard dilutes the total solution; like running in sand you move forward each time, but your reference point moves farther back.

• I worked out the equations for 5ml injections of 3 std concentrations in 500ml of stream sample. This can be a significant source of error for this method of CF.T derivation, especially at higher background EC.T values.

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EC.Ti (uS/cm)

%E

rror

[NaCl] std (mg/l):4000



Measured %Error:0.25 l Sample

Measured %Error:0.5l Sample

Measured %Error:1l Sample

Assuming 5ml increments of std into 500 ml of streamwater and distilled water with 2.2 uS/cm equal to 0.0055 mg of ionic salt (1100 ppm).

Same results are obtained from any initial volume and standard injection volume

AR s Calibration Factor Correction (in progress)

• The bias is positive, CF.T is overestimated; Q is proportional to 1/CF.T so it produces estimates of Q that are lower than true.

• The correction to the error I’ve worked out (for distilled water solute) to be:

si

si

s

i

s

si

si

sii

s

si

si

s

i

i

si

s

si

si

si

s

i

i

si

si

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s

i

i

si

si

ass

true

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Vm

m

m

m

mm

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VVm

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mm

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mV

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VV

mVV

mm

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mV

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VV

mm

TEC

VV

m

TEC

V

m

VV

mm

TCF

TCFE

1

1

11

.

.

1.

.1%

0.

.

][

][

s

i

s

i

si

si

TEC

TEC

Salt

Salt

mV

Vm

s

imeasuredtrue TEC

TECTCFTCF

.

.1..

Assuming the increase in mass for each injection is only the mass from the added NaCl

A more accurate representation of the mass for each standard injection (i is initial in sample, s is std

injection; will change subscripts in V2.0)

AR s Draft Metadata (1/2)

Field Description Required?

Creek The creek sampled Required

Site The site Required

Crew The people who did the measurement Required

Date and time of injection Date and time of slug injection Required

Q (m3/s) Measured flow Required

error in Q (m3/s) Uncertainty in flow estimate No

% error in Q Percent uncertainty in flow Required

% error in CF Estimated uncertainty in CFT (uncertainty in calibration slope) Suggested

% error in mass Uncertainty in mass (%) Suggested

% error in area under curve Uncertainty in area under curve used to calculate Q (%) Suggested

mass of salt added (g) or Volume (L) Mass of salt added, or volume of brine added (%) Required

Harmonic Vel (m/s) An accurate measure of the stream velocity Suggested

Centroid Vel (m/s) A measure of stream velocity based on the centroid of the pulse Suggested

Peak Vel (m/s) A measure of stream velocity based on the peak in the pulse Suggested

CF.T ((g/L)/(uS/cm)) Calibration slope Required

Mean background (μS/cm) Average background conductivity Required

Water temperature (deg C) Water temperature during measurement Required Liquid used to make calibration injection solution Stream or distilled water Required Conductivity of water used to make calibration injection solution needed for correction factor Required

Date Calibration Solution Mixed Required Date of last Lab service / Calibration of EC Sensor Required

Cell Constant in Range Required

Tw in range (two points) Required

• Metadata required to assess quality (uncertainty) of measurement• Useful to have to determine sources of error, better understand the measurement

AR s Draft Metadata (2/2)

• If uncertainty cannot be assessed, a nominal uncertainty is assumed, ±15-30%.

Field Description Required? uncertainty in background cond (uS/cm) Uncertainty in background conductivity (uS/cm) Suggested uncertainty in calibration factor ((g/L)/(uS/cm)) Uncertainty in calibration factor ((g/L)/(uS/cm)) Suggested Type of temperature compensation used during data collection Non-linear (which one if known), linear, or none Required Reference temperature used for temperature compensation

Usually 25 or 20 degrees, temperature data are normalized to Required

Scaling factor used for linear calibration only applicable if linear calibration used Required Concentration of solution added during calibration (g/L)

The concentration of the solution, or amount added if a brind is used Suggested

Amount of pure stream water used for calibration (L) Amount of stream water used during calibration Suggested

Calibration Data The calibration data used to develop the CFT slope Required

Distance pulse travels Distance between injection point and probe Suggested

Start salt wave When the pulse started (injection time) Suggested

end salt wave When the pulse was considered to end Suggested

start pre-pulse background Start of the time period used for the background data Suggested

end pre-pulse background End of the time period used for the background data Suggested

start post-pulse background Start of the time period from after the pulse used for the background data Suggested

end post-pulse background End of the time period from after the pulse used for the background data Suggested

start of record viewed No

end of record viewed No

Type of background: Describe type of background, e.g. constant, or time varying Suggested

Time series of salt wave The actual salt pulse Required

Time series of background The background conductivity values used, need time series if time varying Required

AR s Estimate of Uncertainty

)()(

)..()..(.

)(

)..()..(.

)(

.)..(

maxmin

min

max

QQQQQ

TCFTCFtTECTECTEC

mmQ

TCFTCFtTECTECTEC

mmQ

TCFtTECTEC

mQ

N

i BGBGi

NaClNaCl

N

i BGBGi

NaClNaCl

N

i BGi

NaCl

• It’s unlikely that all errors would align. It’s good to do repeat measurements, and repeat CF.T measurements, for a given stage to determine the repeatability of the measurement.

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1/31/13 17:02 1/31/13 17:09 1/31/13 17:16 1/31/13 17:24 1/31/13 17:31 1/31/13 17:38 1/31/13 17:45 1/31/13 17:52 1/31/13 18:00

Elapsed Time (s)

CT(u

S/c

m/o

C)

C (

uS

/cm

)

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1

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9

10

C Background C (uS/cm/oC) Background CT (uS/cm) Alt_Baseline ALT CT T (oC)

Measured Uncertainty %Uncertainty

Salt (kg) 0.231 0.001 0.4%

CF.T (mg/l/(uS/cm) 0.46 0.013 2.8%

EC.T GS (uS/cm) 33.4 0.1 0.3%

Area (uS/cm*s) 2427 86.4 3.6%

Q (m3/s) 0.21 0.015 7.1%

Qmax (m3/s) 0.22

Qmin (m3/s) 0.20Qstdev (m3/s) 0.014 6.8%

AR s ~Fini

• Questions? (Ask Andre, I need a nap)

Documents

Salt Dilution Uncertainty and Proposed Metadata Requirements CWRA Conference Vancouver Gabe Sentlinger Mar 7, 2013