Emerson Process Management 3081 pH/ORP Three-wire RTD, RTD Resistance Values Temperature 3K Balco

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