Measurement Computing CIO-EXP-GP User Manual

Page 22

Voltages which exceed the ±5V range are in bold italics in the table above. Table 5-5 shows the
temperature at which the reading is clipped (the maximum readable temperature for thermocouple types
at a given gain).

Table 5-5. Maximum Readable Temperatures with A/D on ±5V Range

548°C

1,450°C

1,450

576°C

1,450°C

1,450

80°C

287°C

660°C

900°C

900

115°C

350°C

350

121°C

484°C

1,232°C

1,250°C

1,250

95°C

366°C

750 °C

750°C

750

X1000

X250

X100

X10

Max readable temp vs Gain

Max °C

Type

From these tables, you can determine that if you want to use a J-type thermocouple to make a reading of
700 degrees, the gain should be set at 100. This yields a resolution of 0.48 degrees C per bit.

5.5 Setting the Gain

Once you have determined the gain required for your application, set the gain of the CIO-EXP-GP using
the following guide.

Amplification for ALL channels (board output gain) is switch selectable (S17) for X1 or X2.5.

Input amplification for EACH CHANNEL is switch selectable (CH0 through CH7) for X1, X10, X100 or
X1000. A user-specified gain may be set by supplying a precision resistor at position RX### and setting
the “U” option on switch CH ## to ON.

5.5.1

Setting the Board Gain

10
V

X2
.5

0.5
V

S17

Output Gain Switch

There is a switch on DIP switch block S17 (Figure 5-5) labeled
X1 and X2.5. Sliding this switch down amplifies the output of
the multiplexers by 2.5. The factory default position (up) has a
gain of 1 (unity).

The X2.5 gain switch is useful in some thermocouple
measurements. If you desire a voltage gain of 2.5, 25 or 250, set
this switch down. Recommended gains for thermocouples are
between X10 and X200.

Figure 5-5. Output Gain Switch Location

The effect of this switch is multiplicative with respect to the individual channel gains. For example, if
you have set an input channel gain to X100 and the board output gain to X2.5, the signal is amplified by
250 before it reaches the A/D board.

5.5.2

Setting the Channel Gain