MODEL 3081 pH/ORP

SECTION 12.0

 

TROUBLESHOOTING

B. Check the sensor.

Refer to the wiring diagrams in Section 3.0 to identify the RTD leads. Disconnect the RTD leads and measure the resistances shown in Figure 12-3. The measured resistance should agree with the value in Table 12-1 to within about 1%. If the measured resistance is appreciably different (between 1 and 5%) from the value shown, the discrepancy can be calibrated out. See Section 8.5.

FIGURE 12-3. Three-wire RTD

Consult the table for resistance-temperature data. Lead resistance is about

0.05ohm/ft at 25°C. Therefore, 15 feet of cable increases the resistance by about 1.5 ohm. The resistance between the RTD return and RTD sense leads should be less than 2 ohms.

TABLE 12-1. RTD Resistance Values

Temperature

Pt 100

Pt 1000

3K Balco

 

Resistance

Resistance

Resistance

0°C

100.0 ohms

1000 ohms

2670 ohms

10°C

103.9 ohms

1039 ohms

2802 ohms

20°C

107.8 ohms

1078 ohms

2934 ohms

25°C

109.6 ohms

1096 ohms

3000 ohms

30°C

111.7 ohms

1117 ohms

3067 ohms

40°C

115.5 ohms

1155 ohms

3198 ohms

50°C

119.4 ohms

1194 ohms

3330 ohms

60°C

123.2 ohms

1232 ohms

3472 ohms

70°C

127.1 ohms

1271 ohms

3594 ohms

80°C

130.9 ohms

1309 ohms

3726 ohms

90°C

134.7 ohms

1347 ohms

3858 ohms

100°C

138.5 ohms

1385 ohms

3990 ohms

If a connection is open or shorted and it should not be, the sensor has failed. Replace the sensor.

If the RTD is different from what was expected, for example, the sensor contains a Pt 100, not a Pt 1000 RTD, reset the jumper and reconfigure the software to match the actual RTD

If the measured resistances are acceptable, go to step C.

96

Page 109 Page 111
Page 110
Image 110
Emerson Process Management 3081 pH/ORP instruction manual Three-wire RTD, RTD Resistance Values Temperature 3K Balco
Page 109 Page 111
Top Page Image Contents