To understand the scaling options and coefficients, please refer to this article

https://support.rheonics.com/en/support/solutions/articles/81000391533-scaling-sme-parameters


In the file table attached you will find the Modbus registers associated with each of the measurement parameters provided by SMET. 

To be able to calibrate you will need to work on the holding registers (Modbus Functional command FC3)

Parameter List is as follow: 

Index

Parameter

0

viscosity median / 5 points

1

density median / 5 points

2

temperature median / 5 points

3

Kinematic Viscosity

4

density average / 5 points

5

V - viscosity raw

6

D - density raw

7

T - temperature raw

8

f - resonant frequency (Hz)

9

fc - compensated resonant frequency (Hz)

10

df - damping (Hz)

11

Tc - Coil temperature (°C)

12

viscosity median and last good

13

density median and last good

14

Displays of maps value from Modbus register 512

15

Displays of maps value from Modbus register 514

16

Displays of maps value from Modbus register 516

17

Te – Estimated Temperature (from internal temperature Algorithm)

18

Tp- Temperature from PT1000 sensor present in sensor

19

Parameter calculated from scripting 0

20

Parameter calculated from scripting 1

21

Parameter calculated from scripting 2

22

Ratio


There are two methods to scale using Modbus registers. 


Method 1: The sensor is in the reference fluid. 

In this case we are assuming that the sensor is already dipped in the reference fluid. 


Offset Calibration

  1. Write (any value) to the register identified as Sample 0. This will instruct the SME to take a measurement and store it as that sample. 
  2. Write the reference value, this is, the value expected, in the register Lab 0. 
  3. Write the value 1 (offset calibration) in the register "supported_types". This will make the offset calibration according to the values in Lab 0 and Sample 0. 
  4. To see the calibration results, read the "current coefficients" registers.
  5. To use the factory or user calibration coefficients as the current ones in use write the values 1 or 2 in the "Select Mode" register. On read, this register returns 0 value.

Slope Calibration

In this case we need to take two samples, in theory these samples should be taken at different conditions. For example, different temperatures of a calibration fluid. 

  1. Write (any value) to the register identified as Sample 0. This will instruct the SME to take a measurement and store it as that sample.
  2. Write (any value) to the register identified as Sample 1 (at a different condition from sample 0)
  3. Write the reference values, these are, the values expected, in the registers Lab 0 and Lab 1 respectively. 
  4. Write the value 2 (slope calibration) in the register "supported_types".
  5. To see the calibration results, read the "current coefficients" registers.
  6. To use the factory or user calibration coefficients as the current ones in use write the values 1 or 2 in the "Select Mode" register. On read, this register returns 0 value.


Method 2: Direct calculation of scaling coefficients

You can use the equations from this article 

https://support.rheonics.com/en/support/solutions/articles/81000391533-scaling-sme-parameters to calculate the C0 and C1 coefficients, if you have previous knowledge of the Laboratory and sample values taken by the sensor. 


You can write these coefficients in the registers: 

C0 = current_coeff[0] and C1 = current_coeff[1]