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Sensoray Model 425 Instruction Manual Page 18

Gain Programming

Digitizer gain may be set to unity or higher by means

of a programming resistor. All analog input channels

have the same gain.

Gain is programmed by installing a resistor at position

R8. The value of resistor R8 can be calculated for any

arbitrary gain using this formula:

To prevent thermally-induced gain errors, R8 should

have a low temperature coefficient — preferably 50

ppm/C or less.

The table below shows required R8 values for various

gains using standard 1% resistor values. The listed gain

values are approximate and may be trimmed to exact

values as described in the next section.

As shipped from the factory, digitizer gain is set to

unity (R8 not installed).

Gain Trim

Digitizer gain may be trimmed by adjusting

potentiometer R1. This trimmer provides an adjustment

range of approximately percent.

Offset Trim

Digitizer offset may be trimmed by adjusting

potentiometer R2. This trimmer provides an adjustment

range of approximately . Since this adjustment

may alter circuit gain, offset should be trimmed before

adjusting gain.

(ohms)

Gain Input Range

Unipolar Bipolar

Open 1 0 to +10V -5 to +5V

49.9K 2 0 to +5V -2.5 to +2.5V

12.4K 5 0 to +2V -1V to +1V

5.49K 10 0 to +1V -500 to +500mV

2.61K 20 0 to +500mV -250 to +250mV

1.00K 50 0 to +200mV -100 to +100mV

499 100 0 to +100mV -50 to +50mV

249 200 0 to +50mV -25 to +25mV

100 500 0 to +20mV -10 to +10mV

49.9 1000 0 to +10mV -5 to +5mV

49400

Gain1–

-------------------=

6mV

Input Connections

Each analog input channel makes two connections to

the board as a differential pair. The digitizer measures

the voltage across any such pair.

Input common-mode voltage — the voltage at either

input relative to the ISAbus five volt return (GND) —

should not exceed volts. Minor excursions beyond

this limit may cause measurement errors. Significant

excursions may cause damage to digitizer circuitry.

Refer to the specifications for further details.

All analog input sources should be referenced to

ISAbus GND. If you are connecting an isolated source

(a source not referenced to GND), you should tie one

side of the source to GND. Since analog input channels

are differential pairs, it doesn’t matter which side is

connected to GND.

Connector Pinout

All analog inputs connect to connector P2. This

connector is shared by analog input and analog output

functions. The table below describes that portion of P2

related to analog input functions. Note that the GND

signals are related to both analog input and output

functions.

Connector P2: Analog I/O

Chan Pin Name Function

0 2 ADC0+ + input

4 ADC0- - input

1 6 ADC1+ + input

8 ADC1- - input

2 10 ADC2+ + input

12 ADC2- - input

3 14 ADC3+ + input

16 ADC3- - input

4 18 ADC4+ + input

20 ADC4- - input

5 22 ADC5+ + input

24 ADC5- - input

6 26 ADC6+ + input

28 ADC6- - input

7 30 ADC7+ + input

32 ADC7- - input

33,34,

38,39,

GND Analog

common

1 2 ... 15 16 17 18 19 20 21 22 23 24 25 ... 33 34

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