ADC-20/ADC-24 Terminal Board User Guide DO117-5
Issues: 1) 2) 3) 4) 5) 8.11.05 Created by JB. 13.12.05 p10: added 0V connection to thermocouple schematic. 22.3.06 p11: removed C1. 20.8.07 New logo. 29.9.08 New address. Copyright © 2006-8 Pico Technology. All rights reserved. Pico Technology James House Colmworth Business Park Eaton Socon St. Neots Cambridgeshire PE19 8YP United Kingdom Tel: +44 1480 396395 Fax: +44 1480 396296 Email: sales@picotech.com Web: www.picotech.
Pico Technology ADC-20/ADC-24 Terminal Board User Guide CONTENTS 1 Overview 1.1 Introduction 1.2 Terminals and component sites 1.3 Connecting to the data logger 2 Taking measurements 2.1 Voltage 2.1.1 General 2.1.2 Direct connection 2.1.3 Voltage divider connection 2.2 Current 2.3 Light level 2.4 pH 2.5 Temperature 2.5.1 Introduction 2.5.2 LM35DZ IC 2.5.3 Precision thermistor 2.5.
Pico Technology 1 Overview 1.1 Introduction ADC-20/ADC-24 Terminal Board User Guide The ADC-20/ADC-24 Terminal Board is designed for use with the 8-channel ADC-20 and 16-channel ADC-24 High-Resolution Data Loggers. For simple applications, you can simply connect sensor wires to the screw terminals on the Terminal Board, without the need for soldering.
ADC-20/ADC-24 Terminal Board User Guide 1.2 Pico Technology Terminals and component sites The table below shows the purpose of each of the terminals and empty component sites. Terminal or site 1 to 16 AG DG +5 V and -5 V +2.5 V R1a to R16a R1b to R16b Q1 BNC IC1 Description Connections to ADC channels 1 to 16. Connections to analogue ground. (Note 1) Connections to digital ground. (Note 1) Low-current power supply (up to 2 mA) for sensors, if required. Reference voltage.
Pico Technology ADC-20/ADC-24 Terminal Board User Guide 2 Taking measurements 2.1 Voltage 2.1.1 General When using the ADC-20/ADC-24 Terminal Board with the ADC-20 or ADC-24 to measure voltages, you can connect the voltage source in one of two ways: directly, by plugging straight into the channel, or indirectly, via a voltage divider. 2.1.2 Direct connection For voltage sources measuring from -2.5 V to +2.5 V, use a direct connection to any channel. ADC-20/ ADC-24 terminal board VIN (-2.
ADC-20/ADC-24 Terminal Board User Guide 2.1.3 Pico Technology Voltage divider connection For voltages beyond -2.5 V to +2.5 V, use a voltage divider connection. ADC-20/ADC-24 terminal board ADC-20/ADC-24 unit RA VADC VIN Channel RADC RB AG 0V Voltage divider The voltage that the ADC sees, VADC, depends on VIN and the values of RA and RB, and is given by the following equation: V ADC = V IN × RB R A + RB Choose values of RA and RB so that VADC is approximately +2.
Pico Technology ADC-20/ADC-24 Terminal Board User Guide The following four noise problems are often associated with potential divider circuits: 1. 2. 3. 4. Noise from source voltage. Try fitting a capacitor as described below. RF interference is picked up at high-impedance points. Smaller values for RA and RB may help. Noise on the earth connections. The signal 0 V line is connected to mains earth. Try to avoid this situation.
ADC-20/ADC-24 Terminal Board User Guide 2.2 Pico Technology Current You can use the ADC-20/ADC-24 Terminal Board with the ADC-20 or ADC-24 to measure current. If the current returns through ground, you can use a simple shunt resistor to convert the current into a voltage before measuring with the ADC. The diagram below shows a circuit with a shunt resistor RB.
Pico Technology 2.3 ADC-20/ADC-24 Terminal Board User Guide Light level You can use the ADC-20/ADC-24 Terminal Board with the ADC-20 or ADC-24 to measure light levels. You will also need to use a Light Dependent Resistor (LDR) and a fixed resistor. Use the +5 V output to supply power to the circuit. Use a resistor of around 1MΩ for RA, and place the LDR in location RB. 2.4 pH pH sensor circuit You can use the ADC-20/ADC-24 Terminal Board with the ADC-20 or ADC-24 to measure pH.
ADC-20/ADC-24 Terminal Board User Guide 2.5 Temperature 2.5.1 Introduction Pico Technology If you use the ADC-20/ADC-24 Terminal Board and ADC-20 or ADC-24 with a suitable sensor and the Picolog software, you can measure temperatures accurately.
Pico Technology 2.5.3 ADC-20/ADC-24 Terminal Board User Guide Precision thermistor You can use a precision thermistor in conjunction with the reference output of the ADC-20/ADC-24 to measure temperatures accurately. You will need to consult a table before using PicoLog to convert the voltages into temperature readings. This can be found in Appendix 1. The figures come from the thermistor manufacturer’s data sheet. The diagram below shows how to connect the thermistor to the terminal board.
ADC-20/ADC-24 Terminal Board User Guide 2.5.4 Pico Technology Thermocouple This device has to be used in conjunction with the AD595 IC. The circuitry involved in connecting to the ADC is the most complex of the three types and great care should be taken if choosing this method. The AD595 IC is an integrated thermocouple instrumentation amplifier with built-in cold junction compensation. The diagram below shows how to connect the AD595 IC and the thermocouple to the terminal board.
Pico Technology ADC-20/ADC-24 Terminal Board User Guide Note: The AD595 will require a separate power supply. For full details of the AD595, see the Analog Devices website at www.analog.com. Please observe electrostatic discharge (ESD) precautions when constructing this circuit, to avoid damage to the AD595. The circuit shown can measure temperatures in the range -200°C to +1250°C. The component values are as follows: RA = 44.2 kΩ 0.1% metal film RB = 11 kΩ 0.1% metal film RS = 75 kΩ 0.
ADC-20/ADC-24 Terminal Board User Guide Pico Technology Appendix 1 – Thermistor conversion table Temp. (°C) -30 -20 -10 0 10 20 25 VADC (V) 2.441 2.392 2.311 2.189 2.016 1.794 1.668 Temp. (°C) 30 40 50 60 70 80 90 VADC (V) 1.535 1.264 1.006 0.779 0.593 0.446 0.334 Temp. (°C) 100 110 120 130 140 150 VADC (V) 0.251 0.189 0.143 0.109 0.084 0.065 Temp. (°C) 660 760 780 800 820 840 860 880 900 920 940 960 980 1000 1020 1040 1060 1080 1100 1120 1140 1160 1180 1200 VADC (V) 1.474 1.658 1.695 1.731 1.
