1. ProtoDUNE SP – Slow control temperature gradient monitor
Giovanna Lehmann – Xavier Pons
CERN 11/05/2017

2. IFIC and Hawai CERN/DT temperature readout test setup results.
NI-9238 Data
±500 mV Range, 24 bits resolution
4 simultaneous differential channels, 250Vrms isolation
Error ±0.07% MAX ~ ±30 mK MAX,
Valencia setup ±7.5 mK (Measured in a fixed 25Ω resistor)
Input Impedance > 1GΩ
Current source
Based on Texas Instruments Precise voltage reference application
Hawai calibration: 1000µA ±1µA ~ Max. Error ± 42 mK
Results:
Valencia Calibration: 1000µA ±0.1µA ~ Max. Error ± 4 mK

3. Proposal 1- Temperature Gradient Monitor Readout Hardware - Input PCB.
According the specifications.
The gradient monitors will be connected in the flange by means of DB25 pin connector
So , 6 PT100 (4 wires) x connector
Proposal
To use a PCB for 6U crate size with 4 DB25 connectors
Capacity 24 PT100 per PCB
6U crate size PCB with 4 DB25 connectors. CERN EP/DT

4. Proposal 2. Temperature Gradient Monitor Readout Hardware – Multiplexer.
To multiplex the 24 PT100 signals to the same Analogue Input of the NI 9238 module
Multiplexer from Analog Devices Type ADG707
Datasheet
8 differential signals per multiplexer
3 multiplexers needed for 24 channels connected in cascade
Control bits from NI device

5. Proposal 3. Temperature Gradient Monitor Readout Hardware – Current source
One single current source per 6U PCB, so for 24 PT100
Current source in serial for all PT100
The serialization is done at PCB level
Advantages
Removes the offsets generated by individual current source calibration
Easy calibration
Simple design
Cheaper
Disadvantages
If one PT100 breaks we lose all chain.
This can be fixed by little bridge inside the PCB in the terminals/pad of the damaged PT100

6. Proposal 4. Temperature Gradient Monitor Readout Hardware – Amplifying the working temperature range
With the present configuration we are wasting resolution and unused temperature range
The NI 9238 is measuring from mV that with 1 mA would represent that we measure from 33K to 673 K
The solution is to adapt/amplify the signal between a working or nominal threshold to the measuring range and resolution of the NI module.
With the proposed voltage divider circuit the R2 defines the working range which is amplified.
Proposed Instrumentation amplifier the Texas Instruments INA116
Datasheet
Amplification factor 1 to 1000

7. Proposal 4. Temperature Gradient Monitor Readout Hardware – Amplifying the working temperature range
The following R values provides a working range of the PT100 between 15 Ω and 75 Ω
Corresponds to 65 K to 210 K
If we apply amplification factor = 4 then the 60mV range is amplified to mV range that fits with the measurement range of the NI module.
If we chose narrow working range will have better resolution and accuracy.
Is this useful?

8. DB25 FLANGE CONNECTOR MAPPING – COMPATIBLE WITH FLAT RIBBON TWISTED CABLE

9. DB25 CERN CABLE SPECIFICATIONS

10. Backup

12. Effect of the wire resistance of a PT100 in 4-wires connection in the SP Gradient monitor
Analogue Input Impedance > 1GΩ
Valencia wires Ω/ 100 m; 20 m; Ω x 2; Ω
Cern cable; 85 Ω/km; 20 m; 1.7 Ω x 2; 3.4 Ω
Total Resistance; Ω
Worst case room temperature 298 K; PT100 voltage for 1mA current ~ 110 mV;
Current at the input = 0.11 nA
Voltage drop due to Ω wire resistance ~ 1.9 nV (negligible?)