LI-1400 Description

Simplified Data Logging

Operating the LI-1400 is easy. All functions are selectable from short lists using cursor keys. Commonly used functions like printing and memory management are assigned to a function list on a dedicated key for quick access. Other important functions like instrument setup and data display are also assigned to dedicated keys.

Fast Setup

Channel setup is simplified by the use of log routines that eliminate entering repetitive information. The LI-1400's log routines allow you to enter the logging period, start/stop times and other information in one place, and then apply that log routine to as many channels as required.

Each channel can be individually configured to collect data for logging periods as short as 1 second or as long as 24 hours. Sampling intervals within each logging period are selectable from 1 second to one hour.

For each logging period, data can be integrated or averaged. Alternatively, an instantaneous point reading can be taken at the end of each period. The maximum and minimum readings within the logging period and the time of their occurrence can also be stored.

Math Functions

Channel setup includes choosing from a list of math functions that can be applied to sensor inputs. In addition to sensor input scaling or linearization, several powerful calculations can be performed using math functions:

Math Operators (+, –, •, ÷): Used to combine one input with another through channel addition, subtraction, etc. For example, math operators can determine the ratio of two similar sensors in different environmental conditions, like an LI-190 Quantum Sensor at the water's surface and an LI-192 Quantum Sensor underwater.

Steinhart-Hart Function: Calculates temperature from thermistor type temperature sensors such as LI-COR air and soil temperature sensors.

Saturation Vapor Pressure: Calculated when temperature is input from an air temperature sensor. Dew Point Temperature: Calculates the dew point temperature using signals from the 1400-104 Relative Humidity and Air Temperature Sensor (or equivalent).

Natural Log: Multiplies a constant by the natural log of a channel input. When used in conjunction with math operators, this function can be used to calculate the vertical light attenuation coefficient between two underwater quantum sensors submerged at different depths.

Polynomial: A fifth order polynomial is provided for sensor linearization.

Math Libraries: Five math libraries are available to store values for any of the above math functions. For example, if the same linearization polynomial is to be used for several sensor inputs, storing the polynomial in one of the math libraries eliminates re-entering the polynomial for every sensor.

Math Channels

The logging and calculation capabilities of the LI-1400 are extended by nine math channels. Math channels let you perform additional logging or math routines using any other current, voltage or math channel. For example, if you are logging total daily solar radiation from an LI-200 Pyranometer sensor connected to current channel #1, you can also log hourly integrations or averages from the same sensor by adding the channel #1 input to a math channel and then setting the log routine on the math channel for hourly integrations. Any of the math operators or math functions described above can be used in the math channels as well.

Circuitry

The LI-1400 uses an autoranging, trans-impedance, chopper stabilized amplifier for high resolution (8 picoamp), high accuracy measurements of LI-COR radiation sensors and other sensors with a current output. The high gain amplifier and unique circuit topology gives an extremely low input impedance (< 0.03 ohm) to current sensors, resulting in excellent linearity. Measurement accuracy is enhanced by performing an auto zero and span before every reading (or once per minute with 1-second sampling rate) using a high precision, low drift reference. A precision sigma-delta analog-to-digital converter allows high speed, low noise measurements to be made.

Highly accurate, single-ended voltage measurements are achieved using a precision instrumentation amplifier. Voltage output transducers with low or high output impedance are accurately measured because of very high amplifier input impedance.

Current Channels

The LI-1400 has unrivaled resolution for LI-COR radiation sensors. Current resolution down to 8 picoamps is available through three sealed BNC connectors and two additional channels on the 1400-301 Terminal Block.

The three BNC current channels are designed for type "SA" radiation sensors like LI-COR's LI-190 Quantum Sensor, LI-200 Pyranometer Sensor or LI-210 Photometric Sensor. LI-COR Type "SZ" radiation sensors, with bare wire leads, are recommended for use with the terminal block.

For other sensors, the LI-1400 can measure current up to ± 250 microamps with very high resolution.

Voltage Channels

Four single-ended voltage channels (± 2.5 VDC) provide high input impedance for measuring a wide range of sensors, including LI-COR temperature sensors and humidity sensors. Voltage measurements require the 1400-301 Terminal Block.

1400-301 Standard Terminal Block

Pulse Counting

The LI-1400 has one pulse counting channel for logging total rainfall from a Tipping Bucket Rain Gauge. The counter channel can be accessed through the 1400-301 Terminal Block.

Environmental Operation

The LI-1400's rugged, splash-resistant case protects it from exposure to the environment. Operating temperatures are from -25 to 55 °C. For operation at remote sites, the 1400-201 Vented Instrument Enclosure is recommended to protect sensor connections from rain water and to shade the LI-1400 from direct sunlight.

The LI-1400 is powered by four "AA" batteries which provide over 60 hours of hand-held, instantaneous operation as a meter. For remote logging applications, the 1400-402 external "D" cell battery pack provides over a year of data logging operation from six batteries. To ensure continuous operation, a low battery warning is displayed when the batteries are depleted; a lithium back-up battery protects the memory while changing batteries.

While logging data, the LI-1400 conserves battery life by operating fully powered only when it must sample a given channel. After sampling channels and storing data (if necessary), the LI-1400 automatically returns to a state of low power consumption.

Data Storage

The LI-1400 has 96K bytes RAM for data storage. The storage capacity is dependent on the software configuration.

Table 1. Storage Capacity Examples

Data Output

Windows® communication software is included for:
• Rapid binary data transfer
• ASCII data transfer
• Datalogger configuration changes from the computer.

Stored data can also be transferred to PC-compatible or Macintosh® computers using any terminal program. The LI-1400 data are formatted for easy import into widely used spreadsheet and database software.

Data can be automatically output via the RS-232 port after every logging period. When using short logging periods, this feature allows data capture by a computer with large storage capacity.

Hand-Held Operation

As an autoranging meter, the LI-1400 provides direct read-out for up to three LI-COR radiation sensors without requiring a terminal input block.

The output of a given sensor can be viewed on the LCD display or stored in memory by simply pressing the ENTER key on the keypad (data for all operative channels are stored, along with the time at which the data were logged).

Radiation measurements in water or under changing cloud cover often require an averaged reading of sensor output to obtain the best results. The LI-1400 can display a continuous running average for each sensor. The length of the average is user selectable for each channel. Instantaneous or averaged values for any sensor can also be displayed while the LI-1400 is logging data.