Differential TDR Probe Quick Start Guide Agilent Technologies PS-X10-100 Preliminary version

Printed in Taiwan Oct. 2006 @Copyright 2006 Agilent Technologies, Inc.

Differential TDR probe kit

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Differential TDR probe Kit

Introduction This probe kit has been mainly designed on the hardware platform of Agilent 86100C + 57454A 18GHz TDR module. For high speed application area, more and more requests for differential measurements are needed. With high performance/ stability solutions, for example: wafer level measurement, probe station integration, Cascade/ SUSS is needed. But from package level to PC Board, handy probe is easier for probing purpose. So we, Agilent Taiwan AEO (Application Engineering Organization) has had chance to be involved in widely-inquired application service—“differential probe kit” research and design to fulfill the testing needs. Unlike some of existing probes in the market such as Agilent 113X active differential probe, there are no active components inside, so it acts as passive device or transmission line. Thus, when TDR instrument generates needed test signal, measurement of the reflection portion through probe kit to calculate the impendence will be reached. This probe kit can also be utilized with Network Analyzers for balance devices testing. But additional embedded/ de-embedded process should be added for loss/ phase compensation. Due to time constraint, some of in-planned features were not exactly finalized to our initial expectation at current version (Please see detailed information inside the guide). We have continuously worked out and will focus on the requested solutions by updating them accordingly without specific notice. Several people have dedicated their time and energy throughout the official release of this application service. I am honored to express my deep appreciation herein to Roger Lee, Brian Chi, Kenny Liao, Ming-Fan Tsai, Joe Lin for their tremendous contribution and support.

Peter Kung

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Differential TDR probe kit

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Differential TDR probe Kit

Main probe Overview:

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Differential TDR probe kit

DP3191A disassembly procedures.

Assembled Probe An assembled Differential probe kit appears like the one at left. Where 2 probes are mounted in parallel and bent with approximately 11-degree angles toward each other.

Major Sub-Assemblies Step 1, disassemble upper DP3191A consists of 5 major cover sub-assemblies, these are: 1. Remove the upper & lower 1). Screw for holding upper & covers holding screw “ident lower covers. 1”. 2). Lower cover assembly. 2. Once the screw is removed, 3). Moving block assembly. the upper cover “ident 2” 4). Fixed block assembly. can be lifted up then 5). Upper cover. removed.

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Differential TDR probe Kit

Step 2, disassemble fixed & moving blocks

1.

After the upper & lower covers’ holding screw is removed, the combined fixed & moving block assemblies “ident 1” can be forward sliding and then lifted up.

2.

Be sure that 2 springs “ident 2” not to be dropped apart from their associated rods on the lower cover.

Step 3, disassemble moving block. When performing calibration, the moving block needs to be disassembled. To disassemble moving block, use the L shape Allen Wrench (provided) to rotate the pitch adjustment lead screw counterclockwise until the moving block assembly is completely separated from fixed block assembly.

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Differential TDR probe kit

Moving-block separated from fix-block

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Differential TDR probe Kit

Step 4, further disassemble moving block. Moving block consists of 4 parts, which are: 1). Probe holder. 2). Probe, pre-bent. 3). Probe cover. 4). 4 screws to keep the probe cover in position.

Step 5, further disassemble fixed block. Fixed block consists of 4 parts, which are: 1). Probe holder. 2). Probe, pre-bent. 3). Probe cover. 4). 4 screws to keep the probe cover in position. ** Notice: The pitch adjustment lead screw & sliding rods are not user accessible parts.

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Differential TDR probe kit

Cal-Step 1, moving block cal Perform the moving block calibration, locate: 1). The mounting hole, M2.6 tapped. 2). 2 position holes.

Cal-Step 11, Cal-Extender, front Cal-extender works as a seal part in between the probe and the SMA adapter. Refer drawing at left for the front side details.

Cal-Step12, Cal-Extender, rear Drawing at left depicts the rear side details.

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Differential TDR probe Kit

Cal-Step13, install cal-extender Carefully align the cal-extender 2 positioning pins with the associated positioning holes on the moving block. The drawing below depicts a correct installation.

The cal-extender is properly mated with the moving block. The cal-extender should be remained intake without holding screws.

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Differential TDR probe kit

Cal-Step14, install cal-SMA Similarly, carefully align SMA adapter with cal-extender associated holes. The SMA adapter should be mated with the probe tip.

Cal-Step15, apply screws 2 of M2.6 screws (provided) hold the SMA adapter and cal-extender. Be sure that the short one goes to the top position.

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Differential TDR probe Kit

Cal-extender & SMA adapter firmly installed

Cal-Step16, Fixed block cal Similar to moving block, the fixed block also requires cal-extender and SMA adapter to be installed before it can be calibrated.

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Differential TDR probe kit

DP3191A Differential Probe Kit Parts List

Ident #

Description

Qty

P/N

1

Holding screw, M3, Hex

1

DP3191-0001

2

Lower cover (without springs)

1

DP3191-0002

3

Reset Spring, 10mm

2

DP3191-0003

4

Moving probe holder

1

DP3191-0004

5

Fixed probe holder

1

DP3191-0005

6

Probe, pre-bent

2

DP3191-0006

7

Probe cover

2

DP3191-0007

8

Probe cover screw, M2, 6mm

8

DP3191-0008

9

Upper cover

1

DP3191-0009

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Differential TDR probe Kit

Main probe Overview: ..............................................................................................5 1. Perform Differential Impedance Measurement by TDR ..................................... 17 Equipment Required .............................................................................................................. 17 Setup Procedure ..................................................................................................................... 17 De-skew process .................................................................................................................... 20 Calibration process................................................................................................................. 24 Measurement process............................................................................................................. 32

2. Balance S-parameter Measurement by ENA....................................................... 38 Setup Procedure (Method 1: Using Cal Extender) ................................................................ 38 Setup Procedure (Method 2: Using 4 port De-embedding file) ............................................. 43

3. Appendix............................................................................................................. 46 A. Grounding Enhancement................................................................................................... 46 B. Cross talk performance enhancement (With 4 port De-embedding)................................. 47 C. Typical specification for Differential TDR probe ............................................................. 49

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Differential TDR probe kit

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Differential TDR probe Kit

1. Perform Differential Impedance Measurement by TDR This chapter shows hands on step by step operation with Agilent 86100C+54754A TDR module with firmware version 6.0. Measurement calibration is a process that improves measurement accuracy by using error correction to compensate for systematic measurement errors. This lab shows you how to make practical DUT measurement.

Equipment Required Time Domain Reflector-meter (TDR), Agilent 86100C+54754A PS-X10-100 Differential TDR probe 8 lb Wrench, Agilent 8710-1765 (Optional) Calibration Substrate, Agilent N1020A-K05 (Optional) Other accessories, as ESD protection instruments (Optional)

Setup Procedure 1. Turn on the 86100C mainframe. After you get a display, press the Default Setup key. This will initialize the whole system. 2. Please wait for 20 minutes warm up. 3. Then press {TDR/ TDT} button at front panel let 86100C operated as TDR mode. 4. Under the [calibrate] menu, select [All calibration], then perform left (Or Right) module calibration. And please follows the instructions dialog box from 86100C, you will need 50Ohm and Short connectors during module calibration. 5. Connect two SMA cables with 54754A module. The same as Figure 1-1.

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Differential TDR probe kit

Figure 1-1 Testing environment setup

Figure 1-2 Whole Accessories needed for measurement.

N1020A-K05 Optional

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Differential TDR probe Kit

Figure 1-3 Use 8 lb Wrench to make sure the connection is OK

Agilent 8710-1765 8 lb Wrench (Optional)

Figure 1-4 Use ground cable to connect two probe tips

With Ground Pin added at probe end

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Differential TDR probe kit

Figure 1-5 Use L Shape Allen Wrench to adjust the fit pitch size

Adjust suitable pitch size by Allen Wrench

De-skew process Figure 1-6 At TDR setup, select Differential and De-skew

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Differential TDR probe Kit

6. Connect the cables to Chan1/ Chan2 port of TDR as Fig. 1-1 shows. 7. Then connect Differential TDR probe with grounding pin then adjust the suitable pitch size by Allen wrench as Fig. 1-2 ~ 1-5 8. Then at [TDR setup], please Select Differential and select Diff. TDR and Comm. TDR (Optional) at front panel. Then press [De-skew] as Fig. 1-6 shows. 9. You will see the setting which is similar to Fig. 1-7. Originally, Channel 1 is in Yellow color, Channel 2 is in Green color. That’s the beginning of TDR stimulus response. User should adjust the horizontal plane to check the open positions. 10. Please use Time base knob at front panel to check the cable ending position, please compare Fig. 1-7 and 1-8 86100C’s “Delay”. You will find the ending with timing difference, that’s because of two tip’s adapter/ cable and tip electrical length may not be exactly the same. 11. Adjust the time base scale and delay position, then key in the value to shift the channel 1 & channel 2’s time base. Please verify the timing difference is as closer as 0. Within 1ps difference is recommend. See Fig. 1-10. Figure 1-7 De-skew screen

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Differential TDR probe kit

Figure 1-8 De-skew screen at probe end

Channel 1 & 2 phase shift

Figure 1-9 De-skew screen at probe end

Channel 1 & 2 phase shift

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Differential TDR probe Kit

Figure 1-10 Measure the skew value and key in at 86100C

Check Delta time if it’s within 1ps

Figure 1-11 Overview of TDR probe after de-skew

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Differential TDR probe kit

Calibration process 12. Press Calibration Wizard at left panel of 86100C mainframe, then you will see 5 steps to perform a calibration. See Fig. 1-12 13. The calibration algorithm is based on FFT, during the calibration process, 86100C request you set the right time base for error removing. Please follow the instruction aligned with photos to make the correct measurement. See Fig. 1-13 ~ 1-25. 14. After last step of calibration, there are two 50 Ohm terminators connected to the end of SMA adapter. We usually use these two 50Ohms to verify the system noise level. Please check Fig. 1-26 ~ 1-27. Two 50 Ohms in differential will be 100 Ohm. Usually that should under 1% error, if not, please double check the calibration process is correct or not. 15. After Calibration is complete, you will see an indicator shows “TDR Cal On*”. R1 is as response 1 we selected for Diff. TDR. R2 is as response 2 for Comm. TDR as Fig. 1-27 shows. Now you can connect DUT and change the time base/ vertical scale. Figure 1-12 Perform calibration

Press Calibration Wizard, we need 5 steps for calibration.

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Differential TDR probe Kit

Figure 1-13 Connect DUT to adjust the time base

Figure 1-14 Disassemble main body by L shape Allen wrench

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Differential TDR probe kit

Figure 1-15 Open upper and lower lid

Be careful of the springs, there is no fixed point at lower cover.

Figure 1-16 Use L shape Allen wrench to disassemble two holders

Use another Allen wrench to fully disassemble two block holders.

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Differential TDR probe Kit

Figure 1-17 Connect Calibration Extenders at each end of probe tip

Figure 1-18 Connect SMA adapter along with cal-extender

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Differential TDR probe kit

Figure 1-19 Use Screws to tighten the Cal-extender/ SMA adapter with probe.

Figure 1-20 Use similar steps to connect two probes with SMA adapter.

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Differential TDR probe Kit

Figure 1-21 Connect two SMA shorts at the end of SMA adapters.

** Warning: Please don’t use 8 lb Wrench to tighten the SMA Short. Over pressure at adapters may damage the inner probe tips.

Figure 1-22 Make sure connections are OK then press Next for calculation.

Make sure Channel 1 & 2 connected with two short(s), simple judgment for good connection by viewing yellow line which is opposite while compared with open connection.

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Differential TDR probe kit

Figure 1-23 Then Connect 50 Ohm loads at the end of SMA adapters

Figure 1-24 Confirm the connections are Ok then press Next button.

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Differential TDR probe Kit

Figure 1-25 Press Finish button. Now you can see “Cal ON*” at right corner.

Responses 1&2 (Sdd11/ Scd11 we selected) are On * for showing cable/ adapter error removal.

Figure 1-26 When with 50 Ohm terminated, we use markers for performance verification.

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Differential TDR probe kit

Figure 1-27 Marker value should be closed to 100Ohm with two 50-Ohm linked.

t=0 means the calibration end position, that’s SMA adapter ended.

Measurement process 16. After Calibration is complete and under the tolerance range, please disconnect the Cal extender and SMA adapters then do re-assembly as Fig. 1-28 ~ 1-29. 17. At current version, we didn’t have flush short that can calibrate it to the end of the probe tip. So user should shift 66ps electrical length when using marker. This will be scheduled to be fixed at the future version. See Fig 1-30. 18. When using probe tip to contact DUT, please notice that the contact force is about 100g. The probe itself has springs for force control. Over pressure may crash the DUT and damage the probe tip. Another notice is please vertically touch the DUT. If not; that also easily bends the probe’s tip. Please see Fig 1-31. 19. During measurement, you may see some portion of mismatched ripple occurs when probe tip touches the DUT. The main reason is coming from the different grounds in between probe’s virtual ground and DUT’s ground, which generates inductance contributing the mismatch portion. In order to reduce it, additional ground pin is suggested connecting. 20. Some measurement examples shown from Fig. 1-33 to 1-36.

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Differential TDR probe Kit

Figure 1-28 Disconnect SMA adapters & Cal extenders

Figure 1-29 Re-assemble two blocks together, then put upper/ lower covers back on.

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Differential TDR probe kit

Figure 1-30 Open performance of Differential TDR trace.

Important Notice

Current version’s calibration didn’t have flush short, so after removing SMA adapters, you might see 66ps shift.

Figure 1-31 Use differential probe to test short substrate.

Important Notice

During measurement, please notice that you don’t over drive the contact force, and probe should be as close to vertical position as possible to contact DUT properly.

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Differential TDR probe Kit

Figure 1-32 measurement results with Short substrate

Important Notice Due to grounding plane is different from

Short value

that of DUT, so additional ground pin is needed to reduce mismatch. Please see appendix.

Figure 1-33 Contact 50 ohm for measurement reference.

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Differential TDR probe kit

Figure 1-34 Contact 50 ohm measurement results.

Figure 1-35 Another example for contacting 28 ohm measurement results.

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Differential TDR probe Kit

Figure 1-36 S parameter measurement results with Open ended.

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Differential TDR probe kit

2. Balance S-parameter Measurement by ENA On the other hand, balance S-parameter can also be measured by network analyzer. In this chapter, we utilize E5071B ENA to show the approach. There are two ways to remove probe’s error after 4-port calibration. One is calibrated with cal extender then use Embedded process to rotate the reference plane. Another is calibrated at the SMA cable end without probe inserted during calibration, then use s4p de-embedded the probe’s errors.

Equipment Required Enhancement Network Analyzer (ENA), Agilent E5070B/E5071B PS-X10-100 Differential TDR probe 3.5mm Calibration Kit, Agilent 85033E (Optional) SMA Male to Male adapter, Agilent 1250-1159 (Optional) Calibration Substrate, Agilent N1020A-K05 (Optional)

Setup Procedure (Method 1: Using Cal Extender) 1. Turn on the 86100C mainframe. After you get a display, press the green Preset key. This will initialize the whole system. 2. Please wait for 20 minutes to warm up. 3. Please setup the instrument as needed number of points & IF BW, recommend IFBW = 401. 4. Then under Analysis, select transform (That’s ENA option 010), press “Set Freq Low Pass”, then under Type, choose “Lowpass Step”. Then at format, choose Real. Then you can get the same waveform compared with TDR. If you didn’t have this feature, please skip this step. User could choose phase for verification, too. 5. Please reference the steps as Fig. 1-14 ~ 1-20 for disassembly process. Then connect the 85033E for SOLT calibration. (Additional 3.5 Male to Male adapter may be needed for thru calibration) 6. If you want balance measurement, 4-port SOLT calibration is recommended.

Important Notice

(Although we only use port 1 & port 2 for Differential probe connection), Because balance transfer algorithm also takes other ports’ influence in count, please perform 4-port calibration. 38

Differential TDR probe Kit

Figure 2-1 Use 85033E for calibration process

Figure 2-2 After calibration, use time domain Sdd11 for performance check

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Differential TDR probe kit

Figure 2-3 Then disconnect the cal extender, you will see phase shift at ENA time domain.

Figure 2-4 The lighter line is with cal extender (Reference plane), the darker line is to disconnect the cal extender as shown.

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Differential TDR probe Kit

Figure 2-5 Another way is using phase for verification.

Figure 2-6 Then at ENA Fixture Simulator, select port matching. The file is inside the CD-ROM (Under VNA folder)

Under Port Matching item, please choose s2p file at port 1 & port 2. Then turn ON the Port Matching and fixture simulation.

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Differential TDR probe kit

Figure 2-7 After turning ON Fixture Simulation, the phase error is compensated.

When turn ON fixture simulation is reached, you will see “Sim” indicator change to blue color.

Figure 2-8 Similar way for time domain, before and after it’s embedded.

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Differential TDR probe Kit

Setup Procedure (Method 2: Using 4 port De-embedding file) 7. Another approach is calibrated at the end of the cable. Then insert the differential probe with 4 port de-embedded file. At this method, no cal extender and SMA adapter is needed during calibration. 8. Similar to method 1, 4-port calibration is needed for this setup. But please calibrate it to the cable end. 9. Under ENA front panel Analysis button Æ Fixture Simulator, please select “De-Embedding S4P” as Fig. 2-12. Then press Topology A for port 1 and port 2 de-embedding. (That’s TDR probe’s physical channel, user should assign to the exactly port for de-embedded purpose.) 10. Please choose “4-port_embedding.s4p” for balance S parameter de-embedded then we can use probe for measurement directly. 11. We recommend you use method 1 as standard, because that’s closer to DUT. The main drawback is because port matching doesn’t take cross talk into consideration, so for Common mode measurement as Scd11/ Sdc11. We recommend you use method 2 for measurement. With S4P de-embedded file, Channel 1 and Channel 2’s cross talk can be improved Figure 2-9 Perform 4-port Calibration by 85033E or E-Cal

Calibration reference plane is built at the cable end.

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Differential TDR probe kit

Figure 2-10 Perform 4-port Calibration by 85033E or E-Cal

Figure 2-11 Before 4 port de-embedded. Please select Topology A

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Differential TDR probe Kit

Figure 2-12 Select s4p file for probe error removal.

Figure 2-13 After de-embedding, we shift the phase and reduce cross talk error.

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Differential TDR probe kit

3. Appendix A. Grounding Enhancement Figure A-1 Please connect clamp at probe’s ground pin.

Figure A-2 Measurement example with ground clamp.

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Differential TDR probe Kit

B. Cross talk performance enhancement (With 4 port De-embedding) 1. Originally, this probe is verified by Agilent N5230A-245 PNA-L and N1930A PLTS software during design process. We use these results for embedded and de-embedded process. But if user wants to get more accurate results, two additional items should be taken into consideration. One is that for two probes’ grounding plane it should as close as possible. Another one is that the probe tip should be as short as possible. 2. For Scd11/ Sdc11 measurements, (Also Sdd11/ Sdd22 will have influence) two probes’ cross talk are very important. Please see Fig B-1 when Signal pin’s length is up to 2mm, with higher frequency up to 12GHz, S21 and S12 will be significant large. That will cause balance S parameters incorrect. 3. If we cut the tip to be 1.5mm, performance is improved up to 20GHz, (Under -20dB for S12/ S21) then the trade off is that the pitch size will be bigger than 2mm. 4. So if user wants to utilize this probe to measure higher frequency and balance parameters, please cut the tip length as shorter as possible. (1.5mm is recommended). Please use method 2 for calibration then choose 4-port de-embedded file (2mm/ 1.5mm De-embedding file is under CD-ROM VNA/Appendix B’s folder)

Figure B-1 Probe tip’s length.

Originally, Diff. TDR probe tip length is 2.5mm

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Differential TDR probe kit

Figure B-2 2mm signal tip length S parameter results

Figure B-3 1.5mm signal tip length S parameter results

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Differential TDR probe Kit

C. Typical specification for Differential TDR probe 1. Pitch size: 1.7mm ~ 5.5 mm 2. Maximum operation Bandwidth: 18GHz 3. Frequency ripple: +/- 1.5dB under 18GHz. (With De-embedded) 4. Channel Cross talk: < -30dB under 10GHz 5. Differential Impedance: 100Ohm. 6. Cable length: 1 meter (Qty = 2) 7. Insertion Loss: 2dB @ 12GHz 8. If any additional questions, please contact: [email protected]

D. TDR probe signal pin strength enhancement In order to enhance the strength and prevent probe tip’s bending, we add tolong material cap in front of the tip. Please tight it up during measurement and release it during calibration.

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