HELP DESK FAQ 1 troubleshooting RTD problems v1.1.pdf
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3D TRASAR BOILER TECHNOLOGY HELP DESK FAQ troubleshooting RTD problems Boiler Help Desk FAQ #1 v1.1 Edited March 24, 2009 by JCB page 1 of 2 The first step in troubleshooting RTD problems is to confirm that the RTD is correctly wired. See the table from page 38 of the v3.2 manual below to confirm that the connections are made properly. 3.3.13 Temperature (RTD) Inputs The 3DT Boiler has three 1000 ohm, platinum RTD inputs. Connection Description Controller Box Board Reference Controller Box Terminal Description Wires Labels/Color RTD Probe 1 TB9 -1 1+ Pos. RTD 1 TC+ com or Red TB9-1 S1+ Positive Sense 1 TC+ or Red TB9-1 S1- Negative Sense 1 TC- or Black TB9-1 1- Neg. RTD 1 TC- com or Black RTD Probe 2 TB9-2 2+ Pos. RTD 2 TC+ com or Red TB9-2 S2+ Positive Sense 2 TC+ or Red TB9-2 S2- Negative Sense 2 TC- or Black TB9-2 2- Neg. RTD 2 TC- com or Black RTD Probe 3 TB9–3 3+ Pos. RTD 3 TC+ com or Red TB9-3 S3+ Positive Sense 3 TC+ or Red TB9-3 S3- Negative Sense 3 TC- or Black TB9-3 3- Neg. RTD 3 TC- com or Black NOTE: For remote RTD’s, or RTD’s that are part of a remote NCSM application, ensure that the connections made between the RTD and the cable extension are either made via a terminal strip or soldered and shrink-wrapped. Wire nuts are not an acceptable means of connecting signal wires! Steps to check the resistance of the RTD to confirm that the RTD is working properly. 1. Determine an approximate temperature for the RTD. For example, an RTD in a FW sample is likely to be greater than 120 °F for the NCSM, although this value is very system specific. The typical temperature of a sample flow after the sample conditioning system is in the 60-70 °F range. 2. Remove the RTD terminal from the controller and measure the resistance between the + and (-) connections as well as the + Sense and the (-) Sense connections. These two resistance readings should be identical and a value greater than 1000 Ω. See the graph on the top of the next page to determine an approximate temperature reading for that specific resistance value. Does this seem like a reasonable temperature based on expectations in step 1? 3. With the RTD terminal still disconnected, measure the resistance between the two positive connections (+ and + Sense). This resistance value should be very small (< 10 Ω) and representative of the inherent resistance of the length of wire running from the controller to the RTD. Next, measure the resistance between the negative connections ((-) and (-) Sense), and compare to the
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HELP DESK FAQ 1 troubleshooting RTD problems v1.1.pdf
Transcript of HELP DESK FAQ 1 troubleshooting RTD problems v1.1.pdf
3D TRASAR BOILER TECHNOLOGY HELP DESK FAQ
troubleshooting RTD problems
Boiler Help Desk FAQ #1 v1.1 Edited March 24, 2009 by JCB page 1 of 2
The first step in troubleshooting RTD problems is to confirm that the RTD is correctly wired. See the table from page 38 of the v3.2 manual below to confirm that the connections are made properly.
3.3.13 Temperature (RTD) Inputs
The 3DT Boiler has three 1000 ohm, platinum RTD inputs. ConnectionDescription
Controller BoxBoard Reference
Controller BoxTerminal
Description WiresLabels/Color
RTD Probe 1 TB9 -1 1+ Pos. RTD 1 TC+ com or RedTB9-1 S1+ Positive Sense 1 TC+ or RedTB9-1 S1- Negative Sense 1 TC- or BlackTB9-1 1- Neg. RTD 1 TC- com or Black
RTD Probe 2 TB9-2 2+ Pos. RTD 2 TC+ com or RedTB9-2 S2+ Positive Sense 2 TC+ or RedTB9-2 S2- Negative Sense 2 TC- or BlackTB9-2 2- Neg. RTD 2 TC- com or Black
RTD Probe 3 TB9–3 3+ Pos. RTD 3 TC+ com or RedTB9-3 S3+ Positive Sense 3 TC+ or RedTB9-3 S3- Negative Sense 3 TC- or BlackTB9-3 3- Neg. RTD 3 TC- com or Black
NOTE: For remote RTD’s, or RTD’s that are part of a remote NCSM application, ensure that the connections made between the RTD and the cable extension are either made via a terminal strip or soldered and shrink-wrapped. Wire nuts are not an acceptable means of connecting signal wires!
Steps to check the resistance of the RTD to confirm that the RTD is working properly. 1. Determine an approximate temperature for the RTD. For example, an RTD in a
FW sample is likely to be greater than 120 °F for the NCSM, although this value is very system specific. The typical temperature of a sample flow after the sample conditioning system is in the 60-70 °F range.
2. Remove the RTD terminal from the controller and measure the resistance between the + and (-) connections as well as the + Sense and the (-) Sense connections. These two resistance readings should be identical and a value greater than 1000 Ω. See the graph on the top of the next page to determine an approximate temperature reading for that specific resistance value. Does this seem like a reasonable temperature based on expectations in step 1?
3. With the RTD terminal still disconnected, measure the resistance between the two positive connections (+ and + Sense). This resistance value should be very small (< 10 Ω) and representative of the inherent resistance of the length of wire running from the controller to the RTD. Next, measure the resistance between the negative connections ((-) and (-) Sense), and compare to the
3D TRASAR BOILER TECHNOLOGY HELP DESK FAQ
troubleshooting RTD problems
Boiler Help Desk FAQ #1 v1.1 Edited March 24, 2009 by JCB page 2 of 2
previous reading. These two values should be identical. For example, the wiring for an RTD that is wired directly to the controller on the same skid has a resistance of approximately 0.5 Ω. A resistance greater than 10 ohms likely means that there is either a poor connection or that the RTD is faulty.
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Temperature, Degree F
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Figure 1: Plot of resistance vs. temperature reading.
NOTE: If the temperature is reading incorrectly and there has been the recent addition of a self-powered analog input to the system, the analog input may be wired backwards with the positive output of the sensor going to the negative input of the 3DT Controller and vice versa. (See page 37 of the manual for wiring diagram.) This causes a problem within the internal circuitry of the system as the RTD and 4-20 mA Analog Inputs are non-isolated. This incorrect wiring scheme generally results in the RTD temperature reading lower than expected. For example, a test showed that a temperature reading of 75 degrees °F decreased to 48°F and a reading of 196°F decreased to 70°F with the additional of an incorrectlywired self-powered analog input.
