Xylem H-4280 - Manual (Page 5)

Chapter 1
Introduction
H-4280
Introduction 1-1
1.0 Introduction
The W ATER LOG ® Model H-4280 is a 12-bit, 8-channel, analog input module. The module is an intelligent
SDI-12 “sensor” and can provide measurement data in engineering units such as feet or meters.
The H-4280 is easy to use and works with any data recorder/logger with a SDI-12 interface. The module
is powered from the +12V wire of the 3-wire SDI-12 bus. The SDI-12 (Serial Digital Interface 1200–baud)
is ideal for data logging applications with the following requirements:
Battery powered operation with minimal current drain
Measurement data is transmitted digitally over long cable lengths without error
Multiple sensors on a simple three-wire cable
Up to 250 feet of cable between a sensor and the data recorder (Use of a H-423, SDI-12
to RS485 or H-4500 fiberoptic media converter extends the range to 1000's of feet)
The H-4280 has the following features:
Works with any SDI-12 compliant data logger
8-analog input channels
Supports unipolar (0-5V), bipolar (±5V) and differential (0-5V & ±5V) operation.
12-bit A/D makes up to 700 measurements per second
Precision 5.0V reference output for sensor excitation
Sensor warmup time (excitation) is programmable
Low power sleep operation (<100 A)
Programmable data averaging
Programmable slope, offset and format settings for each of the 8-channels
Built in extended SDI-12 commands for setup and configuration.
Plug-in terminal connectors
1.1 Description
The H-4280 is primarily used to interface simple analog sensors to a SDI-12 compliant data logger. Many
sensors such as potentiometers, thermistors, and pressure sensors can be connected directly to the H-4280.
Each channel can be configured with a y=mX+b linear equation to convert the input voltage into user units
such as temperature, pressure, feet or meters. The linear equation has a slope (m) term and an offset (b)
term. At the factory the slope is set to 1.00 and the offset to 0.00, with these values the measurement will
be in units of Volts. The linear equation will work for sensors such as potentiometers, shaft encoders and
4-20mA transducers with linear outputs. The y=mX+b equation will not work with thermocouples,
thermistors and other sensors having a non-linear response. For these sensors, leave the slope = 1.0, offset
= 0.0 and perform the more complex math operations in your data logger.
1.2 Input Settings
When the data logger issues an aM! command to initiate a measurement, the H-4280 makes 8-
measurements, one for each channel. Each channel can be configured to make Unipolar/Bipolar and
Single/Differential measurements. The results of the 8-measurements are placed in the sensor buffer and
can be collected with aD0! and aD1! commands.