iLink / DS-4483 Technical Note 1

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HydroTel 2000 Technical Note No. 1 - iLink / DS-4483 Standard Program Analogue Sensor Scaling Method Change Effective from:

Standard Logger Program iLink

Version Log350x Version 2.5.1.4

Overview The DS-4483 datalogger standard program has had several updates to better match increasing user expectations and an ever-expanding range of instrumentation. One change in particular, although seemingly minor, has meant a discontinuity in backward compatibility. Therefore, if upgrading a DS-4483 from an earlier version, it is vital that any analogue sensors are rescaled. The change described affects the scaling of analogue input sensors only. All other supported sensor types (SDI-12, pulse, counter, derived etc) are not affected. Note that CSI 107 type thermistor probes are also unaffected, despite these being an analogue sensor. The reason behind this change is a response to multiple requests from users wanting a common scaling methodology with other dataloggers. Although on face value, the older method seemed more "user friendly", as the user could enter real engineering values, it is felt that this change is fully warranted. It actually simplifies the internal algorithm and also allows the user to view the raw input voltage on the LCD during field calibration. The examples below show the difference between the old and new methods used. It assumes the logger has been set up to measure a (hypothetically perfect) 10 metre pressure transducer with a 0-5V output range. The sensor is outputting a 2.5V signal representing a 5 metre depth. The user wants the logger to display and process the water level value in millimetres.

HydroTel 2000 Technical Note No1: - Issue 1 – 21st November 2002

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Old Scaling Method (Versions prior to Log350x) 1. The logger took a measurement of the input signal and obtained a raw analogue-todigital converter (ADC) value (which was always between 0 and 4095 for a zero to full scale input). In this "perfect" example the ADC value will be 2048. 2. The logger then scaled this to actual engineering units (Water Level) by applying the four user settable scaling parameters from the iLink template: RawMax RawMin EUMin EUMax

(Minimum Raw ADC Value) (Maximum Raw ADC Value) (Minimum Engineering Units) (Maximum Engineering Units)

0 4095 0 10000

Water Level = ADC * ( (EUMax - EUMin) / ( RawMax - RawMin)) 5000 = 2048 * (10000 - 0) / (4095 - 0))

New Scaling Method (Versions from Log350x onwards) 1. The logger takes a measurement and obtains a value in actual volts (V). 2. The logger then scales this to actual engineering units (Water Level) by applying the user settable multiplier and offset parameters from the iLink template and/or the LCD/keypad in the datalogger: Offset Multiplier

0 2000

Water Level = (V * Multiplier) + Offset 5000 = (2.500 * 2000) + 0 Finally for both methods, any user settable offset obtained from the calibration process is applied to give the desired relative level in the same way as the old method.

Calculating Multiplier and Offset Multiplier Offset

= =

(Max E.U – Min E.U) / (Max Input Volts – Min Input Volts) Min E.U

= =

(10000mm – 0mm) / (5V – 0V) 0V

e.g: Multiplier Offset

HydroTel 2000 Technical Note No1: - Issue 1 – 21st November 2002

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iLink Changes On connecting to the logger for the first time, select the "Logger Program >= Log350x” check box on the Device Info page shown below. This setting is stored in the profile and is merely used to change the edit fields and labels on the "Scaling " tab in the Logger Configuration screen

If upgrading a logger, rather than setting up one for the first time, you will need to calculate and enter the Multiplier and Offset fields correctly. They will be displaying the old Maximum E.U and Minimum E.U values before the change is made. The pictures below show the old and new scaling tab pages.

HydroTel 2000 Technical Note No1: - Issue 1 – 21st November 2002

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DS-4483 Changes Apart from the scaling algorithm change described above, the calibration screen (accessed by the F2 key from the Setup Menu) has been enhanced. This now shows actual measured input voltage to the right of the scaled engineering units. Pressing the Down Arrow key from here will then show the multiplier and offset values as defined in the template. These can be altered by pressing the F1 or F2 key respectively. NOTE: To input negative values, it is necessary to first press the Clear key, then the negative (-) key, then the digits. The need to do this will be eliminated in a future firmware release (current version is VL/2.12). The Up Arrow key will return to the calibration screen from the Multiplier/Offset screen.

HydroTel 2000 Technical Note No1: - Issue 1 – 21st November 2002