Geokon 3810A Manuale utente

Document Revision: E| Release date: 3/18/19

Model 3810A

Addressable Thermistor String

Instruction Manual

WARRANTY STATEMENT

GEOKON warrants its products to be free of defects in materials and workmanship,

under normal use and service for a period of 13 months from date of purchase. If the

unit should malfunction, it must be returned to the factory for evaluation, freight

prepaid. Upon examination by GEOKON, if the unit is found to be defective, it will be

repaired or replaced at no charge. However, the WARRANTY IS VOID if the unit shows

evidence of having been tampered with or shows evidence of being damaged as a

result of excessive corrosion or current, heat, moisture or vibration, improper specifi-

cation, misapplication, misuse or other operating conditions outside of GEOKON’s

control. Components that wear or are damaged by misuse are not warranted. This

includes fuses and batteries.

GEOKON manufactures scientific instruments whose misuse is potentially dangerous.

The instruments are intended to be installed and used only by qualified personnel.

There are no warranties except as stated herein. There are no other warranties,

expressed or implied, including but not limited to the implied warranties of merchant-

ability and of fitness for a particular purpose. GEOKON is not responsible for any

damages or losses caused to other equipment, whether direct, indirect, incidental,

special or consequential which the purchaser may experience as a result of the instal-

lation or use of the product. The buyer’s sole remedy for any breach of this agreement

by GEOKON or any breach of any warranty by GEOKON shall not exceed the purchase

price paid by the purchaser to GEOKON for the unit or units, or equipment directly

affected by such breach. Under no circumstances will GEOKON reimburse the

claimant for loss incurred in removing and/or reinstalling equipment.

Every precaution for accuracy has been taken in the preparation of manuals and/or

software, however, GEOKON neither assumes responsibility for any omissions or

errors that may appear nor assumes liability for any damages or losses that result

from the use of the products in accordance with the information contained in the

manual or software.

No part of this instruction manual may be reproduced, by any means, without the written consent of GEOKON. The

information contained herein is believed to be accurate and reliable. However, GEOKON assumes no responsibility

for errors, omissions or misinterpretation. The information herein is subject to change without notification.

The GEOKON® wordmark and logo are registered trademarks with the United States Patent and Trademark Office.

TABLE OF CONTENTS

1. INTRODUCTION............................................................................................................................................1

2. INSTALLATION..............................................................................................................................................2

2.1 THERMISTOR STRING ....................................................................................................................2

2.2 HARDWARE REQUIREMENTS..................................................................................................2

2.3 TTL / USB TO RS-485 CONVERTER.....................................................................................2

3. MODBUS RTU PROTOCOL ..............................................................................................................3

3.1 INTRODUCTION TO MODBUS..................................................................................................3

3.2 MODBUS RTU OVERVIEW...........................................................................................................3

3.3 MODBUS TABLES ...............................................................................................................................3

3.4 READING 3810A SENSORS.......................................................................................................3

4. MODBUS & CAMPBELL SCIENTIFIC DATALOGGERS...................................5

4.1 DESCRIPTION .........................................................................................................................................5

4.2 WIRING.........................................................................................................................................................5

4.3 SAMPLE CR6 PROGRAM..............................................................................................................5

4.4 SAMPLE CR1000 PROGRAM WITH REQUIRED MODEL 8020-38

ADDRESSABLE BUS CONVERTER .......................................................................................6

5. TEMPERATURE CALCULATION.................................................................................................7

5.1 STEINHART-HART COEFFICIENTS.......................................................................................7

5.2 FLOATING POINT RESISTANCE READINGS (PREFERRED METHOD)..7

5.3 RAW ADC (ANALOG TO DIGITAL CONVERTER) READINGS ........................7

6. SOFTWARE ........................................................................................................................................................8

APPENDIX A. SPECIFICATIONS ......................................................................................................9

A.1 POWER .........................................................................................................................................................9

A.2 COMMUNICATION .............................................................................................................................9

A.3 MECHANICAL .........................................................................................................................................9

A.4 MEASUREMENTS ..............................................................................................................................9

FIGURES

FIGURE 1: MODEL 3810A ADDRESSABLE THERMISTOR STRING ................................1

FIGURE 2: MODEL 3810A ADDRESSABLE THERMISTOR ..............................................1

FIGURE 3: MODEL 3810A-3 END TERMINATOR ............................................................2

FIGURE 4: MODEL 8020-38 ADDRESSABLE BUS CONVERTER ....................................2

FIGURE 5: PC TERMINAL PROGRAM SCREEN CAPTURE ..............................................4

III

TABLES

TABLE 1: 3810A WIRING .................................................................................................... 2

TABLE 2: RAM STORAGE .................................................................................................... 3

TABLE 3: EXAMPLE QUERY - TRIGGER MEASUREMENT ............................................... 3

TABLE 4: EXAMPLE QUERY - FLOATING POINT RESISTANCE READING ..................... 4

TABLE 5: EXAMPLE RESPONSE - FLOATING POINT RESISTANCE READING .............. 4

TABLE 6: DATALOGGERS WITH RS-485 CONVERSION .................................................. 5

TABLE 7: DATALOGGERS WITHOUT RS-485 CONVERSION........................................... 5

TABLE 8: 3810A THERMISTOR STRING TO RS-485 TO TTL CONVERTER WIRING....... 5

MODEL 3810A ADDRESSABLE THERMISTOR STRING | INTRODUCTION | 1

1. INTRODUCTION

Model 3810A thermistor strings are temperature sensors that combine NTC

thermistors with digital Modbus RTU communication for ease of setup and use.

Each thermistor sensor contains a small printed circuit board assembly (PCBA)

with a thermistor and circuitry for communication and analog to digital

conversion. These sensors are assembled with cable using customer-specified

spacing. Then each sensor is encapsulated in a protective housing, creating a

finished thermistor string.

Thermistors are semiconductors that behave as resistors with a high (usually

negative) temperature coefficient of resistance: they are thermal resistors. The

thermistor beads are made from a mixture of metal oxides encased in epoxy or

glass. The beads are small in size and extremely robust, with a high degree of

stability over a long life span. The accuracy and interchangeability of the

thermistor bead used on the 3810A is ±0.07 °C, within the temperature range of

0 °C to 50 °C.

The cable consists of two twisted pairs, each wrapped with aluminized Mylar foil

and a single drain wire. There are four conductors: power, ground, and the two

differential RS-485 lines for communication. A short-circuit between any of the

four conductors will render all sensors in the string inoperable. Likewise, a break

in the cable would render inoperable all sensors below the break. However,

because the 3810A uses a bus topology, failure of any single thermistor sensor

does not affect any of the other sensors.

The sensors are polled individually via industry standard Modbus RTU (Remote

Terminal Unit) commands.

FIGURE 1: Model 3810A Addressable Thermistor String

FIGURE 2: Model 3810A Addressable Thermistor

2| INSTALLATION | GEOKON

2. INSTALLATION

2.1 THERMISTOR STRING

Uncoil the thermistor string and place it in the installation medium. For

installations in which the string will be in contact with soil, rock, etc., take care

to prevent damage to the cable and sensor. The termination assembly at the end

of the string is made with a 1/4-20 x 1/2” deep threaded hole in it. This allows for

a weight or cord/rope to be attached for assisting with the installation. The

maximum pulling force that can safely be applied to the string is 20 lb.

FIGURE 3: Model 3810A-3 End Terminator

Table 1 shows the function of each of the conductors of the instrument cable.

TABLE 1: 3810A Wiring

2.2 HARDWARE REQUIREMENTS

Communications: RS-485, half-duplex

Baud Rate: 115200

Power: 12.0V ± 20% @ 1.2mA/sensor

2.3 TTL / USB TO RS-485 CONVERTER

GEOKON manufactures the Model 8020-38 Addressable Bus Converter for

connecting addressable strings to personal computers, readouts, dataloggers,

and programmable logic controllers. The converter acts as a bridge between

USB/TTL-capable readers and the GEOKON RS-485-enabled sensor strings.

FIGURE 4: Model 8020-38 Addressable Bus Converter

For more information, please refer to the Model 8020-38 Addressable Bus

Converter Instruction Manual.

3810A String Description

Red String Power

White Communication RS-485+

Green Communication RS-485-

Black Ground

Shield Analog Ground

Indice

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