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Brainboxes AD-945 Supplementary Manual

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ATB Reference
ANALOG
TERMINAL
BOARD
MANUAL
2.01 EDITION
AUGUST 1997
Intro-1

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Summary of Contents for Brainboxes AD-945

  • Page 1 ATB Reference ANALOG TERMINAL BOARD MANUAL 2.01 EDITION AUGUST 1997 Intro-1...

  • Page 2: The Layout Of This Manual

    Thank You For Buying The Analog Terminal We proudly present the Analog Terminal Board. The Analog Terminal Board is the easiest and tidiest way of connecting real world devices to our range of AD1200 Analog to Digital acquisition systems. Your board is designed and manufactured in England, and our policy is one of complete support to our dealers and direct to our users.

  • Page 3: Table Of Contents

    ATB Reference Contents. ________ _ Introduction. The Analog Screw Terminal Board Fused Power Rails. Attaching The Optional LED’s. Jumpers Settings, W1-W4. Differential Analog Inputs, 8DI. 4-20mA Current Inputs. Thermocouple Cold Junction Compensation. List Of Figures. Figure 1-1. Optional LEDs Figure 1-2. Jumper Table. Figure 1-3.

  • Page 4: The Analog Screw Terminal Board

    Analog Terminal Board ANALOG SCREW TERMINAL BOARD. Introduction. ___________ _ This manual explains the functions and features of the Analog Screw Terminal Board. Apart from bringing the AD1200 cards i/o lines out to easily accessible terminals the Analog Terminal Board is designed to take several user fitted components.

  • Page 5: Attaching The Optional Led's

    Reference Provision for LED indication of TTL digital line levels. Provision for cold junction compensation circuitry, CJC, for thermocouple inputs. ATB-CJC version only! Fused Power Rails. ________________ _ The +12Volt and -12Volt power lines are lead via 62mA fuses to the 2nd terminal of the Digital i/o port rails. It is recommended that not more than 50 mA is drawn from the PC! Earlier style PC’s may have a low wattage power supply and therefore LESS power should be drawn...

  • Page 6: Differential Analog Inputs, 8Di

    Analog Terminal Board _______________________ Jumpers Settings, W1-W4. There are four jumpers on the ATB. The functions are summarised in Figure 1-2. Jumpers W1 and W2 are used only in with the thermocouple cold junction compensation circuitry. W1 connects the CH0 input to the cold junction circuit whilst W2 connects the CH0 return line to ANALOG ground.

  • Page 7: Figure 1-3. Resistor Table, Di Inputs

    Reference these are 10k 1/4 watt nominal value, though anything in the range 1k-100k would be adequate. Installing these resistors causes the return side of each channel to be referenced to the system ground, SYS GND. The return resistors for channels 0 to 7 are R14, R10, R6, R2, R15, R11, R7 and R3 respectively.

  • Page 8: Figure 1-4. Resistor Table, Se Inputs

    Analog Terminal Board turning the 4-20mA inputs into voltages. Set the A/D card for 8 channels differential input, Unipolar 0-5 Volt range. Install the current shunt resistors. These should be high precision 250 Ohm resistors, 0.01% or better. These give an output voltage of 250mV per mA.

  • Page 9: Thermocouple Cold Junction Compensation

    Reference Thermocouple Cold Junction Compensation, CJC. ___________________________________________ _ Much of the following information was gleaned from the Analog Devices "Transducer Interfacing Handbook - A Guide to Signal Conditioning." Edited by Daniel H. Sheingold ISBN 0- 916550-05-2, see especially Chapter 7 "Thermoswitches and Thermocouples".
  • Page 10 Analog Terminal Board Reference fitted. Thermocouple Outputs. A thermocouple is the junction between two dissimilar metals, the TYPE of thermocouple depends on the metals used. Thermocouples generate an output voltage that varies with temperature, as observed initially by T. Seebeck in 1821. Thus by accurately measuring the voltage generated by a thermocouple the temperature is precisely known.
  • Page 11 Reference __________________________________________ Figure 1-5. Voltage as Function Of Temperature. TEMP degrees Centigrade -200 -100 1000 1100 1200 __________________________________________ Figure 1-6. Temperature as Function Of Voltage. VOLTAGE milliVolts - 5.000 The Need For Cold Junction Compensation. Any junction bewteen dissimilar metals forms a thermocouple, the connection point between the junction abd measure temperature col Using The Cold Junction.
  • Page 12 Analog Terminal Board Channel 0 Return lines. R26, need not be inserted when the CJC circuitry is in use. When jumpers are not placed across the W1 and W2 shorting headers the cold junction compensation circuitry does not effect the analog terminal board or the AD1200 card at all.
  • Page 13 Reference Calibrating The Cold Junction. The cold junction compensation circuit can be calibrated simply in the following manner. Place a precision voltmeter across the W1 and W2 jumper pins. Adjust potentiometer R23 with a screw driver so that the voltmeter reads 0.5mV times the ambient temperature.

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