Resistance Temperature Detectors
Essentially a resistor with a well-characterized temperature/resistivity function. Driven with a small (~0.1mA) current, a voltage (~10mV) is read and interpreted as a temperature. RTDs are implemented in LTX-β in the center stack (8), the beam scrapers (8), and the beam dump (11).
The RTDs used in LTX are 100Ω devices conforming to the IEC-60751 standard by Omegafilm, which corresponds to a Thermal Coefficient of Resistivity (TCR) type 3851, recognized in National Instruments documentation as "Pt3851."
Nomenclature
Although we took "RTD" to stand for "resistive thermal devices," they are more widely known as "resistance thermometers" or "resistance temperature detectors."
RTD Arrays
Center Stack
Details...
| RTD | Calibration | In-Situ | Acquisition | |||||
|---|---|---|---|---|---|---|---|---|
| ID |
z |
φ |
Gus# |
TBath (°C) |
T-TBath (°C) |
T-Tavg @21°C (°C) |
NI board |
NI input |
| 1 |
-37.5cm |
0 |
x |
x |
x |
+0.23 |
Slot 2 | #19 |
| 2 |
-27.5cm |
0 |
x |
x |
x |
+0.03 |
Slot 3 | #0 |
| 3 |
-15cm |
0 |
x |
x |
x |
-0.15 |
Slot 3 | #1 |
| 4 |
-2.5cm |
0 |
x |
x |
x |
-0.11 |
Slot 3 | #2 |
| 5 |
2.5cm |
0 |
x |
x |
x |
x |
Slot 3 | #3 |
| 6 |
15cm |
0 |
x |
x |
x |
x |
Slot 3 | #4 |
| 7 |
27.5cm |
0 |
x |
x |
x |
x |
Slot 3 | #5 |
| 8 |
37.5cm |
0 |
x |
x |
x |
x |
Slot 3 | #6 |
Beam Scrapers
Details...
| RTD | Calibration | In-Situ | Acquisition | |||||
|---|---|---|---|---|---|---|---|---|
| ID |
z |
φ |
Gus# |
TBath (°C) |
T-TBath (°C) |
T-Tavg @20°C (°C) |
NI board |
NI input |
| U1 |
7cm |
16 |
25 |
79.5 |
+0.5 |
-0.22 |
Slot 2 | #0 |
| U2 |
7cm |
20.5 |
18 |
80.1 |
-0.1 |
-0.58 |
Slot 2 | #1 |
| U3 |
7cm |
24.5 |
16 |
80.4 |
-0.4 |
-0.33 |
Slot 2 | #2 |
| U4 |
7cm |
28 |
13 |
80.5 |
-0.5 |
-0.57 |
Slot 2 | #3 |
| L1 |
-7cm |
16 |
19 |
80.1 |
-0.1 |
+0.53 |
Slot 2 | #4 |
| L2 |
-7cm |
20.5 |
5 |
85.1 |
-0.1 |
+0.33 |
Slot 2 | #5 |
| L3 |
-7cm |
24.5 |
2 |
84.1 |
+0.9 |
+0.34 |
Slot 2 | #6 |
| L4 |
-7cm |
28 |
1 |
83.3 |
+1.7 |
+0.51 |
Slot 2 | #7 |
Beam Dump
Details...
| RTD | Calibration | In-Situ | Modeling | Acquisition | |||||
|---|---|---|---|---|---|---|---|---|---|
| ID |
z |
φ |
Gus# |
TBath (°C) |
T-TBath (°C) |
T-Tavg @19°C (°C) |
Vincent# |
NI board |
NI input |
| 1 |
4.9cm |
234 |
21 |
79.6 |
+0.4 |
+0.24 |
x |
Slot 2 | #8 |
| 2 |
4.9cm |
238 |
20 |
78.5 |
+0.5 |
-0.13 |
x |
Slot 2 | #9 |
| 3 |
4.9cm |
242 |
7 |
83.0 |
+2.0 |
-0.32 |
x |
Slot 2 | #10 |
| 4 |
0" |
234 |
8 |
83.1 |
+1.9 |
-0.20 |
x |
Slot 2 | #11 |
| 5 |
0" |
238 |
6 |
83.0 |
+2.0 |
+0.23 |
x |
Slot 2 | #12 |
| 6 |
-4.9cm |
234 |
3 |
83.6 |
+1.4 |
+0.20 |
x |
Slot 2 | #13 |
| 7 |
-4.9cm |
238 |
24 |
79.9 |
+0.1 |
+0.39 |
x |
Slot 2 | #14 |
| 8 |
-4.9cm |
242 |
22 |
80.1 |
-0.1 |
+0.21 |
x |
Slot 2 | #15 |
| 9 |
4.9cm |
231 |
29 |
80.0 |
+1.5 |
+0.40 |
x |
Slot 2 | #16 |
| 10 |
0" |
231 |
33 |
80.0 |
+2.8 |
-0.66 |
x |
Slot 2 | #17 |
| 11 |
-4.9cm |
231 |
34 |
80.0 |
+2.9 |
-0.37 |
x |
Slot 2 | #18 |
Acquisition
The RTDs are all digitized in two PXI 4357s in rack <X> in L209 in real time, accessed by a LabView script on Hermes. This is currently a work-in-progress.
Eventually, data will be stored to the tree. The LabView display updates at roughly 1Hz, but the frequency (in Hz) of digitization can be set at the front panel. Since the thermal response of the components diagnosed by the RTDs is on a much longer timescale than that of the plasma, the LabView VI which reads from the RTD digitizer board begins recording when a new shot is made, and stores at End of Cycle to /p/ltxdata/RTDs in an LVM file. This file is read by an automated script, which then transfers the raw (temperature vs time) and analyzed (total deposited energy) RTD data to the tree.
Calibration
ASK GUS AND JOHN
Wiring Errors
Dec. 2018 testing of the RTDs found that all beam dump sensors and several center stack sensors were not functioning.
As of Jan. 2nd 2019 the error appears to be miswiring at the connector (either air-side or vacuum-side), transposing positive current in with negative voltage out (or an equivalent error) on each of the 11 beam dump RTDs. This is based on measuring resistance between each of the four wires, and checking parity by measuring voltage with a second voltmeter.
As of Jan. 3rd 2019 the corresponding wires have been swapped at the terminal strip, and documentation has been updated to correctly identify wire colors and their associated RTD leads and terminal positions.
NB: The above corrections are based on the assumption that the RTD is an ideal Kelvin sensor so that: 1. the current channel and voltage channel are interchangeable, and 2. it is non-polar and only parity between current-in and voltage-out polarities is important. The manufacturer documentation has nothing to say explicitly about this assumption, although the fact that all RTD diagrams show only two leads and 4-wire models are described as "extension lead wires" indirectly supports it.
Remaining Work
As of Jan. 3rd 2019 the RTDs still need to be tested. The upper half of the center stack RTD array is known to have open loop wiring faults.
Related Pages
RTD photodocumentation gallery
Diagnostics
Magnetics (Local): Reentrant array | Toroidal array | Saddle coils | Shell eddy sensors
Magnetics (Areal): Poloidal flux loops | Loop voltage | Diamagnetic loop | IP Rogowski
Spectroscopy: Thomson scattering | ChERS | X-ray spectroscopy | Spectrometry | Vacuum UV spectroscopy
Microwaves: Reflectometry | Interferometry
Physical Probes: HFS edge probes | LFS SOL probes | RFEA
Operational Diagnostics: Ion gauges | Coil current monitors | Thermocouples | RTDs
