SOW.pdf

Statement of Work

1. Introduc on/Background: Current CTA systems that are commercially available in the US from companies like Dantec Dynamics and TSI Incorporated do not meet our required specifica ons for high-bandwidth, research-grade systems applicable for high-speed flow applica ons. The commercial systems are now overly simplified for plug-and-play type applica ons and are more tailored for university laboratories. This new CTA system promises the flexibility needed for expert users. We have commercial CTAs currently on the market in our organiza on that are more applicable to lower speed flows and the older commercial units with higher performance are no longer on the market. We have a empted to work with these manufacturers in past years to deliver a system for our current needs, but we have been unsuccessful. The older commercial systems from the previously named companies that met our needs are no longer available and the units we have are failing due to age (units are 30+ years old).

2. Scope of Work: This project will result in a custom-built 3-channel constant temperature anemometer (CTA) system that promises to address our needs for supersonic / hypersonic flow measurements.

3. Objec ves: Provide high-bandwidth flow measurements in supersonic / hypersonic flow regimes while maintain low system noise. Goal is to provide a CTA system with be er overall performance than commercially available systems in the US.

4. Descrip on of the Work/Contractor Tasks: Project is to develop a 3-channel CTA system based on the earlier demonstra on system developed by the contractor (award 80NSSC21P2134). See the accompanying specifica on document for more details.

5. Deliverables: The primary deliverable for the proposed project is a three-channel CTA system consis ng of three CTA Modules and a single Power Supply-Oscillator Module.

Addi onal deliverables will include a user manual along the lines of the one delivered with the demonstra on system. Work schedule is expected to be approximately 6 months from contract award.

Constant Temperature Anemometer (CTA) System

General specifications proposed by LaRC group for a CTA unit

25 July 2023

1) Probe sensor resistances: 2 ohm (platinum-plated tungsten) – 10 ohm (platinum-rhodium Wollaston wire) cold. Maximum value at overheat ratio of 2: ~20 ohms. The cable + lead resistance is typically between 2.5 and 2.6 Ohms. The cable lengths (RG58 type cable) are typically 20 to 25 m. The leads lengths (~0.060” dia coax cable or RG178 type cable) are typically between 50 to 64”. Both cable and lead are 50 Ohm impedance.

2) Maximum overheat ratio, Rhot/Rcold = 2.0.

3) Probe operating environments: 60 to ~500 F.

4) Bandwidth: +400 kHz.

5) Cable lengths: design for 20-25 meters to achieve optimal performance at these lengths. The system should still work with longer or shorter cables, so we should have enough latitude in the system adjustments, but the achievable frequency response may be impacted. The 1:1 bridge is supposed to be fairly forgiving of different cable lengths assuming the probe and external arm are well matched.

6) Bridge ratio 1:1 (top of bridge resistors equivalent on cold and active sides).

7) Operate with an external arm (comprised of a cable, lead, and manually adjustable resistor) to balance the probe arm (comprised of a matched cable and lead, and a hot-wire sensor).

8) Oscillator: in addition to internal square wave injection, add ability to inject external signal to enable manual tuning of frequency response. For external injection and small amplitude values required for injection, add feature like a voltage divider to enable the use of standard waveform generators without external amplitude attenuation.

9) Noise: Low. (Target voltage noise due to amplifier of same order as Johnson noise of probe resistor in bandwidth of interest). If everything is done right, the system noise can be predicted on the basis of the Johnson noise associated with all the resistors in the system and the amplifier noise. The minimal achievable noise goes as f^2 with frequency. If we see that behavior, we know the system has been well designed. At high frequencies the signal is dominated by the f^2 noise.

10) Overall system operation compatible with multiple channels.

Target specifications for 3-channel CTA unit (addresses changes from demonstration system)

25 July 2023

1) Number of channels: System to consist of three CTA channels with cabled connections to a Power Supply/Oscillator module.

2) Power Supply/oscillator module: This module will contain a +/-15.0 V at 1.5 A linear supply. It will be mounted in a housing with the same size front panel as the demonstration unit, but with a depth similar to the CTA housings (and the demonstration CTA housing).

3) Rack mounting/overall packaging: The overall packaging of V.2 will be similar to the demonstration system and will not be designed for mounting in a standard equipment rack. Vented top and bottom panels will be combined with stand-off feet to allow natural convection cooling of the electronics in both the CTA and Power Supply modules.

4) Top Rails/handles: The top rails employed to mechanically integrate the modules will extend beyond the sides of the outermost CTA and Power supply modules to provide mounting points for handles. To reduce the bench-space footprint of the overall assembly, the handles will fold down.

5) Wiring protection panel: A panel will be attached to a bottom rail, extended behind the modules to protect the cabling running between each CTA module and the Power Supply module. The panel will be approximately one-third the height of the modules.

6) Circuit boards: The CTA circuit board will be printed. The initial Power Supply module circuit board may be hand-wired or printed (preferred).

7) Square-wave oscillator: Internal square wave signal will be made bi-polar with maximum amplitude of +/- 0.5 V. (Current adjustment range for internal oscillator is ~10 mv-2.74 V.)

8) Square-wave amplitude adjustment: Amplitude adjustment sensitivity will be increased so setting knob does not need to be at the bottom of the range.

9) Static sensitivity: Static sensitivity will be mitigated by improving the method of securing shielded power connectors. This will avoid spurious bridge shut-downs.

10) Inductor: A dual-coil adjustable unit, similar to the one fabricated in the recent project, “Dual-coil inductor module project V.2, shipped on 6/29/2023, will be mounted on the printed circuit board of each CTA module. An adjustment screw thread of #5-40 will be used. The axis of the inductor will be perpendicular to the front panel and the adjustment screw will be accessible through the front panel. The adjustment will be located at the midpoint between the Probe and Bal Leg BNC connectors.

11) Output BNCs: A total of two dedicated BNC connectors will be provided for monitoring the bridge output voltage, one to be installed as in the demonstration unit, on the front panel (Output BNC 1), and one to be installed on the back panel of the CTA module (Output BNC 2). The BNC connector 3 will allow monitoring of signals selected using the rotary switch on the front panel. It will be located on the back panel of the CTA. Output BNC 1 on the front panel will be moved down to provide more space above it for the bridge offset and gain controls.

12) Bridge Offset adjustment: This control will be moved from its current location below Bal Leg BNC to a location above the Output BNC 1.

13) Gain setting location and type: This will be moved from its current location below Output BNC 1 to a location far enough above Output BNC 1, to avoid getting bumped when cabling is mated/detached.