User Manual

Global Water Instrumentation
13
Sensor Data Format
Analog sensor data is transmit ted as a 10-bit number in the range of 0-1023. A
calibration equation is applied to the raw data number at the database to scale the
sensor reading in t he appr opr iate range and engineering units. Digit al input
accumulator s c ount input events from things like tipping bucket rain gauges and flow
monitors. The accumulator is transmitted as a 11-bit number in the range of 0-2047
and calibration f ac tors are also used t o s c ale the data. Once reaching 2047, the
accumulator c ounter rolls back t o zero with the next count. Digital status inputs
transmit all channel data in a s ingle s tatus regist er with 1-bit for each channel, one or
zero, t r ue/f als e, on/off, open/closed, etc. Digital control outputs als o hav e their
status trans m itted in a single regist er with 1-bit for each output channel.
Because digital stat us inputs and control out puts only need one data bit to transmit
their st ate, these channels c an be c om bined into one data value. The state of up to
4 status inputs are combined into one status r egis ter in binary for m at, channel one
shown by bit one, channel two with bit two, etc. In the same manner , the curr ent
state of the control outputs is trans m itted in a single status r egis ter. Register
contents r eturned as 0011 (binary) shows channels 1 and 2 High (ON), and channels
3 and 4 Low (OFF). Features in the databases allow the m apping of these bits to
text labels .
Calibration Numbers
Data values are transmitted to the hosting databas es as r aw data numbers. This
number is scaled to the desired engineering units (EU) by fir st m ultiplying it with a
scaling factor (Multiplier) , then adding an off s et (Adder). These numbers ar e the
coeffic ients in a straight line equat ion: EU = Adder + (Mult iplier * RawData). These
calibration number s ar e entered into the databases and t he s c aling takes place as
the data com es in. Thus, all the calibration is done at the database, independent of
the field station. There is an Excel spr eads heet calculator for finding these
calibration f ac tors that can be downloaded from our webs ite at globalw.com/support.
Some examples are also given in Appendix B.
Another impor tant feature is available for calcul ating data. When the raw data has
been adjusted to the proper engineering units using the st r aight line equation
discussed above, the database calibr ations allows for additional mathem atical
operations. For example; these equations can be flume or weir equations for