GRAS 246AE SysCheck2 Software Development Kit Instruction Manual

SysCheck2™ Software Development Kit

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Instruction Manual

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Introduction

SDK for 246AE and 246AO microphones overview

246AE, 246AO specification

Syscheck2 behavior

Syscheck2 has a very well-defined coupling of the test signal to the microphone, due to precision coupling capacitor with a guarded signal path from the generator in close proximity, resulting in reliable test results over a wide frequency range due to no stray coupling of test signal to preamplifier, polarization voltage or in transmission cable.
Syscheck2 generator level has very little influence from of temperature, the Syscheck2 measurement therefore reflect the change of capacity of the microphone. The membrane capacity has a slight frequency dependency, but not enough to verify the frequency response. Causes to change in microphones capacity are change in temperature, change in polarization voltage, change membrane tension and damages to the microphone housing or the membrane. Testing the capacity at medium frequencies e.g. 250Hz, can verify the general sensitivity of the microphone. The Syscheck2 can reveal sensitivity change due to temperature, but not to change in pressure or humidity.

Syscheck2 usages

In the simple use where environment condition has not changed, a relative check with Syscheck2 @250Hz before and after will ensure that the sensitivity has not changed more than 4 times the Syscheck2 change in dB (in other words if the Syscheck2 has changed 0.05dB the microphone sensitivity is expected to be within 4*0.05dB ~ ±0.2 dB.
Since the change can originate from different things, such as change in membrane tension, change in mechanical or change of charge, the sign of the change cannot be determined.
If temperature, ambient pressure, and humidity has changed, the sensitivity of the microphone might also have changed. Initial when the reference Syscheck2 measurement is made the temperature, ambient pressure and humidity can read from 246AE or 246AO and memorized together with the measurement. If only temperature has changed the Syscheck2 verification can be corrected for this.

• using a 1/3 octave narrow band measurement the noise level of 60dB during test, will typically influence less than 0.2dB.
• If the microphone is calibrated to -25.5dBV/Pa @ 23°C, the sensitivity correction of 246AE microphone @ 35°C is -0.01*(35-23)dB = -0.12dB, the sensitivity @ 35°C will be -25.5+(- 0.12)dBV/Pa = -25.62dBV/Pa.

1. Together with a calibration of the microphone, make a Syscheck2 reference measurement:
   a. Measure the Syscheck2 level, e.g -27.20dBV
   b. Read the temperature from the TEDS, e.g. 25°C These data can be used to verify the microphone later.
2. In the field when a verification of the microphone is needed:
   a. Measure the Syscheck2 level, e.g -27.03dBV
   b. Read the temperature from the TEDS, e.g. 35°C
   c. Calculate temperature corrected verification 1): SC_level_corrected = SC_level_measured – ((Ta)
   2* TC2 + Ta * TC – ((RT)
   2* TC2 + RT * TC) )
   → SC_level_corrected = -27.03 – ((35)2 * -96.0E-6 + 35 * 16.1E-3 – ((25)2 * -96.0E-6 + 25 * 16.1E-3) ) = -27.13 dB

246AE, 246AO firmware 1.8

Description of the interactions between integration software and Syscheck2 mic set

Abstract:

This chapter is made to help system integrators to retrieve information and communicate with a Syscheck2 microphone set. It is a step by step instruction based on three different functions that needs to be included in the integration software.
Notes: In this description we use a 246AE. The procedures are unchanged*) when using another type of Syscheck2 microphone set (i.e 246AO).
*) only change is for temperature and pressure coefficients
Requirement Specification for User Interface:
Temperature will be handled in Celcius. Unit conversion to Fahrenheit shall only be informal to the user. Acceptance level:
User must be able to select an acceptance level based on a choice list (drop down list?). Current acceptance limit thresholds are; 0.3dB, 0.5dB & 0.8dB
Syscheck2 Result:
User interface needs to show the Syscheck2 result, e.g. with 2 colors; Green & Red depending on the Syscheck2 Level result compared to the acceptance level.

8) Read user data eg.: “246AE {: Pid 00003F RT 23.1 RP 1013 Tc2 – 96.0E-6 Tc 16.1E-3 }”, where t=27.4, p=1008 and h=40 are the newly sensor measured values of temperature, pressure and humidity.
//note: If env is not changed to Env by the sensor during the procedure in 6), environmental data are not updated.
9) Log Env data locally (t, p, h) + standard TEDS information (Model & serial no & sensitivity) + other data of interest (e.g. time stamp or other system integrator parameters
10) Exit DIGITAL mode → Enter ANALOG mode
11) * allow minimum 5 seconds for ANALOG microphone state to stabilize before starting measurement

10) Read user data eg.: “{: Pid 00003F F Env Tc2 -96.0E-6 Tc 16.1E-3 }”
11) Localize Syscheck2 data Tc2, Tc, and derive p and t from Env between “{:” and “ }”, these values are needed for step 13
12) Set RL=measured_SC_level; eg. -26.95 Set RT=t; eg. 21.5Set RP=p; eg. 1013

13) Write TEDS Syscheck2data: “{: Pid 00003F F Env 21.5 1013 RL -26.95 RT 21.5 RP 1013 Tc2 -96.0E-6 Tc 16.1E-3 b3}”
// b3 meaning blue LED ON for 3 seconds, indicating Syscheck2 ref is done.
14) Exit DIGITAL mode → Enter ANALOG mode

1) Enter DIGITAL mode
Only data between “{:” and “ }” in user data is modified in the following. All other TEDS data is preserved.
2) Read from TEDS user data into local string
3) Localize Syscheck2 data Pid, Tc2, Tc, RL, RT and RP between “{:” and “ }”, store each variable locally. If Tc2, Tc, RL, RT and RP is not present in user data, inform user that Syscheck2 data is missing and encourage to perform >>Make Syscheck2 reference<< to clear out” and exit >>Syscheck2<< function.
// If Tc2, Tc, RL, RT and RP are present, we want to proceed and setup TEDS to retrieve env parameters and generate a tone from generator
4) Write string to TEDS user data: “246AE {: Pid 00003F f env 27.4 1008 40 RL -27.00 RT 23.1 RP 1013 Tc2 -96.0E-6 Tc 16.1E-3 G 010 }” ? // F and Env is changed to lower case f and env
5) Exit DIGITAL mode → Enter ANALOG mode

// TEDS user data should now contain “246AE {: Pid 00003F F Env RL -27.00 RT 23.1 RP 1013 Tc2 -96.0E-6 Tc 16.1E-3 G 010 }
9) Read userdata: “Env” and split into t, p and h variables and store locally for use in the following.
10) Calculate SC_level_corrected SC_level_corrected = SC_level_measured – ((t) 2 * Tc2 + t * Tc – ((RT)2 * Tc2 + RT * Tc) )
Note: Tc and Tc2 has been read from Syscheck2 transducer.
Use the following criteria for evaluation whether microphone is within chosen acceptance level: Calculate DSL, which is the distance from recent SC_level_corrected to the microphone Syscheck2 reference level RL. DSL = | SC_level_corrected – RL |

11) ENTER DIGITAL mode and write evaluation to TEDS
// if GREEN: write userdata:
//“246AE {: “246AE {: Pid 00003F F Env 21.5 1008 54 RL -27.00 RT 23.1 RP 1013 Tc2 – 96.0E-6 Tc 16.1E-3 g 010 }”
// If RED: write userdata:
//“246AE {: “246AE {: Pid 00003F F Env 21.5 1008 54 RL -27.00 RT 23.1 RP 1013 Tc2 – 96.0E-6 Tc 16.1E-3 r 010 }”
12) Exit DIGITAL mode

13) Log data (optionally) locally (t, p, h, SC_level_corrected) + standard TEDS information (Model & serial no & sensitivity) + time  On system integrator side
14) Present Syscheck2 evaluation to user.
// Green = Syscheck2 OK, Red = Syscheck2 NOK If microphone sensitivity correction (see notes) is more than 0.2dB then display the message: “It is advised to compensate microphone sensitivity, as change temperature and static pressure since Syscheck2 reference were made may cause a measurement correction of more than 0.2dB”.

NOTES:

• If either one of the following variables Pid, Tc2, Tc, RL, RT and RP are not present in the TEDS user data the Syscheck2 can not be evaluated and should terminate with a note to the user.
• All variables (Pid, Tc2, Tc, RL, RT and RP) can be created by calling >>Make Syscheck2 reference<<
• Background noise should be lower than 65dBspl for 246AE and 77dBspl for 246AO
• The temperature sensor has reduced specifications outside [0…65 °C]
• If the temperature is higher than 85 °C, the env value is set to 85. User should be alerted.
• If the current temperature and atmospheric pressure results in change in microphone sensitivity of more than 0.2dB, since Syscheck2 reference were made, the user should be notified;

Sensitivity correction = |(t-RT)*sensTC + (p-RP)*sensPC |
If Sensitivity correction is more than 0.2dB then display the message :
“It is advised to compensate microphone sensitivity, as change temperature and static pressure since Syscheck2 reference were made may cause a measurement correction of more than 0.2dB”.

RL = Syscheck2 reference level, designate with 2 decimals
RT= Syscheck2 reference temperature, designate with 1 decimals
RP= Syscheck2 reference atmospheric pressure, designate with 0 decimals

Vmeas= measured output from analysator [Vrms], uncorrected for environment.
t = Measured output from the temperature sensor (env)
TC = Syscheck2 temperature coefficient, read from user data
TC2 = Syscheck2 temperature coefficient 2, read from user data

Environment correction coefficients, valid for 250Hz only.

SC_level_corrected = SC_level_measured – ((t)2 * TC2 + t * TC – ((RT)2 * TC2 + RT * TC) )

GRAS TEDS editor SW0051

Example of TEDS with commands in user data: