NIOSH Conformity Assessment Notice 

NIOSH CA 2018-1002

June 2018

 

Intra-Laboratory Comparison of LabVIEWTM Data Acquisition Software to 

replace use of the Gould RS3200 Strip Chart Recorder 
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NIOSH CA 2018-1002

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1 SUMMARY

The National Personal Protective Technology Laboratory (NPPTL), a Division of the National Institute 

for Occupational Safety and Health (NIOSH), is responsible for the approval of respiratory protective

devices in accordance with the regulations contained in Title 42 of the Code of Federal Regulations, 

Part 84 (42 CFR 84).

For more than 15 years, NPPTL has tested Respiratory Protective Devices (RPDs) using the Gould 

Instrument Systems, Inc. model RS3200 strip chart recorder (with carrier amplifier). Gould Instrument 

Systems, Inc. is no longer in business and replacement parts for the RS3200 are no longer available. 

This warranted the development of a new test system to replace the Gould RS3200 strip chart 

recorder.

To address this concern, NPPTL, under a contract with Data Science Automation (DSA), developed a 

personal computer (PC) based system running Microsoft Windows and using National Instruments’ 

LabVIEWTM data acquisition software. Data acquisition and carrier amplifier hardware were also 

incorporated into the new system.

NPPTL’s laboratories in Pittsburgh, Pennsylvania and Morgantown, West Virginia are equipped with the 

new LabVIEWTM based system. Only the Pittsburgh laboratory has the Gould RS3200 system. To 

validate the LabVIEWTM based system, testing was conducted in Pittsburgh and Morgantown using 

NIOSH-approved self-contained breathing apparatus (SCBAs). All units were tested using the Gould 

system in Pittsburgh as well as the LabVIEWTM systems in Pittsburgh and Morgantown. A statistician at 

NPPTL analyzed the results.

Results show that the LabVIEWTM strip chart system is capable of replacing the Gould strip chart 

recorder. Additional benefits of the LabVIEWTM system include automatic data logging and a reduction 

of the subjectivity associated with determining pass/fail results (using the strip recorder).

Subject: Intra-Laboratory Comparison of LabVIEWTM Data Acquisition Software to replace use of 

the Gould RS3200 Strip Chart Recorder 
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NIOSH CA 2018-1002

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2 AUTHORITY

42 C.F.R. Part 84, Respiratory Protective Devices

Subpart H, Self-contained breathing apparatus

Eight NIOSH Standard Test Procedures utilize the Gould RS3200 strip chart recorder:

RCT-APR-STP-0065, Determination of Airflow Resistance of Breath Responsive, Powered AirPurifying Respirators (PAPRs) 

RCT-ASR-STP-0105A, Determination of Airflow-Demand and Pressure-Demand, Type C and CE, 

Supplied-Air Respirators 

RCT-ASR-STP-0106, Determination of Inhalation Airflow Resistance, Pressure-Demand, Type C 

and CE, Supplied-Air Respirators 

RCT-ASR-STP-0117, Determination of Positive Pressure, Closed-Circuit, Pressure-Demand, SelfContained Breathing Apparatus 

RCT-ASR-STP-0120, Determination of Positive Pressure, Open-Circuit, Pressure-Demand, SelfContained Breathing Apparatus 

RCT-ASR-STP-0121, Determination of Rated Service Time, Open-Circuit, Demand and PressureDemand, Self-Contained Breathing Apparatus

RCT-ASR-STP-0135, Determination of Inhalation and Exhalation Breathing Resistance, ClosedCircuit, Demand and Pressure-Demand, Self-Contained Breathing Apparatus 

RCT-ASR-STP-0138, Determination of Safety Relief Valve Operation, Closed-Circuit, Demand 

and Pressure-Demand, Self-Contained Breathing Apparatus 

3 BACKGROUND and SUPPLEMENTAL INFORMATION – INTRA-LABORATORY COMPARISON

Gould Instrument Systems, Inc. is no longer in business, which prompted the question “What do we do 

when our RS3200 strip recorder stops working?” To address this concern, as well as NPPTL’s goal of 

updating test procedures to take advantage of new or emerging technology, NPPTL began 

development of a new test system that could replace the Gould test system. NPPTL awarded a 

contract to Data Science Automation (DSA) for development of a PC based system using National 

Instrument’s LabVIEWTM data acquisition software and LabVIEWTM compatible data acquisition 

hardware. Additional carrier amplifier hardware was also necessary. This new system was developed 

for a Microsoft Windows operating system.
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3.1 Methods

Upon completion of the system development, DSA delivered the LabVIEWTM test setup to NPPTL. The 

system was initially setup at NPPTL’s Pittsburgh laboratory. To verify the LabVIEWTM system produced 

statistically similar results to the Gould system, testing was conducted using two readily available SelfContained Breathing Apparatus (SCBAs), a Scott Air Pak 75 SCBA with a 60-minute cylinder and an MSA 

Firehawk® M7 SCBA with a 30 or 45-minute cylinder. Both units met NFPA 1981-2007. The units were 

tested on the Gould RS3200 system and the LabVIEWTM based system. Figures 1a and 1b show the 

corresponding test setup.

Figure 1a: NPPTL Gould Strip Chart Setup

Figure 1b: NPPTL LabVIEWTM Strip Chart Setup
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The units were tested under baseline conditions as well as under a condition where the zero point was 

adjusted to approximately +0.1 to +0.2 inches of water. This condition caused negative spikes to be 

displayed on the Gould RS3200 that had a minimum detectable area below the zero line. This is critical 

for accepting a negative spike on the Gould system at a speed of 20 mm/sec.

During the testing, the LabVIEWTM strip chart recorder display was adjusted to match the Gould speed. 

It was verified that the minimum detectable negative spikes produced on the Gould recorder were 

logged as negative spikes that met the criteria for being reported and logged as failures. The 

comparison verified that the minimum and maximum pressures recorded during the testing matched 

between the Gould recorder and the LabVIEWTM recorder at a tolerance of +/- 0.05 inches of water. 

The shapes of the breathing curves were also subjectively evaluated to ensure a match between the 

two methods. After this preliminary work was completed, several additional tests were performed on 

other approved makes and models of SCBAs.

All of the aforementioned tests were performed by running the Gould system and the LabVIEWTM

system simultaneously. Results from the two recordings were compared for minimum and maximum 

pressures, and both measurements were within +/- 0.05 inches of water.

After the Gould system and LabVIEWTM system were validated at the NPPTL Pittsburgh laboratory, it 

was time to collect data at the NPPTL Morgantown laboratory. A second LabVIEWTM system, as shown 

in Figure 1b, was setup in the Morgantown laboratory. A detailed test plan was written which included 

the Gould system in Pittsburgh, the LabVIEWTM system in Pittsburgh, and the LabVIEWTM TM system in 

Morgantown.

The test plan included eight SCBAs. Again, these SCBAs were chosen as they were readily available. 

The SCBAs chosen included Sperian-Honeywell (1 unit), Dräger (1 unit), Avon-ISI (1 unit), Interspiro (1 

unit), Scott Health and Safety (3 units), and MSA (1 units). One of the Scott units was adjusted to allow 

the waveform to go slightly negative.
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The test plan that was developed was a full comparison of the Pittsburgh laboratory to the 

Morgantown laboratory. Therefore, the test plan included all five of the current SCBA STPs (0120,

0121, 0122, 0123, and 0124). However, the information provided in this notice is focused on the 

comparison of the Gould system to the LabVIEWTM system. Therefore, the data presented is from STP0120.

Each unit was tested three times. Each unit completed all of the tests at one laboratory before being 

moved to the other laboratory. All of the cylinders were charged using identical settings. The 

facepiece seal to the headform was tested by utilizing a vacuum delay method. The facepiece negative 

pressure was lowered, by vacuum, to below -1.0 inches of water. The time of the vacuum delay from 

-1.0 to -0.8 inches of water had to be less than 15.0 seconds. All tests were completed in the same 

order at both locations.

3.2 Results

Table 1 shows the test results for the Positive Pressure Tests (STP-0120) for each unit tested. As 

mentioned previously, each unit was tested three times on each system. It is also worth mentioning 

again that the units were tested simultaneously on the Pittsburgh LabVIEWTM and Pittsburgh Gould 

systems. The data is shown by unit with the results of each run shown under each system.

The “Gould Difference” column shows the difference between the Pittsburgh systems only (Pittsburgh 

LabVIEWTM – Pittsburgh Gould). The “LabVIEWTM Difference” column shows the difference between the 

LabVIEWTM systems only (Morgantown LabVIEWTM – Pittsburgh LabVIEWTM). 

Table 1: Positive Pressure Test (STP-0120) Data (inches of water)

Positive Pressure Test: RCT-ASR-STP-0120 (results are inches of water)

Sperian-Honeywell

Run

Pittsburgh Morgantown Gould Difference LabVIEWTM Difference

Gould LabVIEWTM LabVIEWTM LabVIEWTM - Gould Morgantown - Pittsburgh

1 0.15 0.10 0.20 -0.05 0.10

2 0.15 0.10 0.20 -0.05 0.10

3 0.15 0.10 0.20 -0.05 0.10
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Dräger

Run

Pittsburgh Morgantown Gould Difference LabVIEWTM Difference

Gould LabVIEWTM LabVIEWTM LabVIEWTM - Gould Morgantown - Pittsburgh

1 0.15 0.10 0.10 -0.05 0.00

2 0.10 0.10 0.05 0.00 -0.05

3 0.05 0.10 0.10 0.05 0.00

Avon-ISI

Run

Pittsburgh Morgantown Gould Difference LabVIEWTM Difference

Gould LabVIEWTM LabVIEWTM LabVIEWTM - Gould Morgantown - Pittsburgh

1 0.50 0.50 0.50 0.00 0.00

2 0.50 0.50 0.50 0.00 0.00

3 0.50 0.50 0.50 0.00 0.00

Interspiro

Run

Pittsburgh Morgantown Gould Difference LabVIEWTM Difference

Gould LabVIEWTM LabVIEWTM LabVIEWTM - Gould Morgantown - Pittsburgh

1 0.40 0.35 0.40 -0.05 0.05

2 0.40 0.40 0.40 0.00 0.00

3 0.35 0.35 0.35 0.00 0.00

Scott NXG

Run

Pittsburgh Morgantown Gould Difference LabVIEWTM Difference

Gould LabVIEWTM LabVIEWTM LabVIEWTM - Gould Morgantown - Pittsburgh

1 0.25 0.25 0.25 0.00 0.00

2 0.20 0.20 0.25 0.00 0.05

3 0.20 0.20 0.20 0.00 0.00

Scott 2.2

Run

Pittsburgh Morgantown Gould Difference LabVIEWTM Difference

Gould LabVIEWTM LabVIEWTM LabVIEWTM - Gould Morgantown - Pittsburgh

1 0.10 0.10 0.10 0.00 0.00

2 0.05 0.05 0.05 0.00 0.00

3 0.05 0.05 0.05 0.00 0.00
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Scott 4.5

Run

Pittsburgh Morgantown Gould Difference LabVIEWTM Difference

Gould LabVIEWTM LabVIEWTM LabVIEWTM - Gould Morgantown - Pittsburgh

1 0.00 -0.05 -0.10 -0.05 -0.05

2 -0.20 -0.20 -0.15 0.00 0.05

3 -0.25 -0.25 -0.10 0.00 0.15

MSA

Run

Pittsburgh Morgantown Gould Difference LabVIEWTM Difference

Gould LabVIEWTM LabVIEWTM LabVIEWTM - Gould Morgantown - Pittsburgh

1 0.10 0.10 0.10 0.00 0.00

2 0.05 0.05 0.10 0.00 0.05

3 0.05 0.05 0.10 0.00 0.05

3.3 Discussion

A statistician at NPPTL analyzed all data. Since each system was tested three times in Morgantown and 

three times in Pittsburgh, this type of data is referred to as “paired replicates” data. The difference

within each run was used for statistical analysis. For comparing the LabVIEWTM data, the difference 

measure (Morgantown LabVIEWTM Data – Pittsburgh LabVIEWTM Data) was used for statistical testing. 

To compare the Gould Data, the difference measure (Pittsburgh LabVIEWTM Data – Pittsburgh Gould 

Data) was used for statistical testing.

Because of the small sample sizes (n=3) for each unit, the Wilcoxon Signed Rank (WSR) test was used to 

test if the difference was zero (p-value is shown in the tables). The WSR test is preferable to a 

parametric test (i.e. Student’s t-test with degrees of freedom = 2) when the sample size is small, 

because the WSR uses exact probabilities and does not require a random sample. Note that the 

smallest possible p-value for this test (with n=3) is 0.25.

There are four possible p-values for the WSR when the sample size is three: 0.25, 0.50, 0.75, or 1.0. 

There can be no differences with a traditionally statistically significant test result (with α=0.05) and if 

one or more of the differences are the same (tied observations) the p-value cannot be calculated. 

However, p-values with the smallest value of 0.25 should be considered as possibly significant 

differences. The estimate of the difference is a non-parametric location estimator known as the 

pseudo-median or Hodges-Lehmann estimator calculated for each unit separately and for all the data 

combined.

For all practical purposes, the estimate of the difference, whether nearly statistically significant or not, 

may be too small to represent any important difference or may be within the measurement error of 
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the laboratory. The estimates of the difference and tests of significance can only provide information 

to aid the determination.

The Kruskal-Wallis test can be used to test if the systems are different. To determine which of the 

systems are different from each other, typically the confidence intervals of the differences can be 

compared. Again, with the small sample size of n=3, the WSR test provides (if there are no ties in the 

data) a 75% confidence interval instead of the more familiar 95% confidence interval. In fact, given 

only three observations, the 75% confidence interval is the same as the range of a sample size of 3, so 

the minimum and maximum of the sample are the same as the 75% confidence limits. This way, there 

is some indication if a particular system tends to have higher measurements in one particular location 

compared to the other systems.

The WSR test on the differences, using all the data for the systems combined, tests if the Morgantown 

laboratory values are different from the Pittsburgh laboratory values. It also estimates the magnitude 

of the difference. This statistic is reported at the bottom of the tables for each test. It is also possible 

to compare the number of positive differences to the number of negative differences to determine if 

there is a tendency for measurements to be higher in one location or the other. This is known as a 

binomial test or sign test. This result should generally agree with the WSR test; but is generally less 

efficient than the WSR test.

Table 2 shows the statistical analysis for the Pittsburgh data only (LabVIEWTM vs Gould). Using the WSR 

test, the results indicate there is no difference between the LabVIEWTM data and the Gould data 

(p=0.1094). The WSR test on the median estimate for the combined data (all units) is 0.00, which 

indicates that the LabVIEWTM data is not statistically different from the Gould data.
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Table 2: Positive Pressure Test (STP-0120) Statistical Analysis (LabVIEWTM vs Gould)

Unit p-value Median Estimate C.I. or Min, Max

Sperian-Honeywell 0.2500 -0.0500 -0.050, -0.050

Dräger 1.0000 0.0000 -0.050, 0.050

Avon-ISI NA 0.0000 0.000, 0.000

Interspiro 1.0000 -0.0125 -0.050, 0.000

Scott NXG NA 0.0000 0.000, 0.000

Scott 2.2 NA 0.0000 0.000, 0.000

Scott 4.5 1.0000 -0.0125 -0.050, 0.000

MSA NA 0.0000 0.000, 0.000

Wilcoxon Signed Rank Test 0.1094 0.0000 95% C.I. = -0.050, 0.050

Sign Test (exact Binomial) 0.1300 - -

Kruskal-Wallis Test 0.2100 - -

Out of the 24 difference estimates (LabVIEWTM – Gould) there were six negative values, 17 zero values, 

and one positive value suggesting that there is a tendency for higher measurements with the Gould 

system.

Examining each of the eight systems separately, the median estimate of the difference was zero 

(indicating no difference between the LabVIEWTM data and Gould data) for five systems (Dräger, AvonISI, Scott NXG, Scott 2.2, and MSA). The median estimate of the difference was negative (indicating 

higher results for the Gould recorder) for three of the systems (Sperian-Honeywell, Interspiro, and 

Scott 4.5). In order, from smallest to largest the system estimates are -0.05, -0.0125, -0.0125, 0, 0, 0, 0, 

and 0 for the respective systems: Sperian-Honeywell, Interspiro, Scott 4.5, Avon-ISI, Scott NXG, Scott 

2.2, MSA. and Dräger.

A Kruskal-Wallis test comparing the difference between the LabVIEWTM data and the Gould data 

indicates there is no statistically significant difference between the two systems (p=0.2100).

Table 3 shows the statistical analysis for the LabVIEWTM data only (Morgantown vs Pittsburgh). Using 

the WSR test, the results indicate that the Morgantown results are higher than the Pittsburgh results 

(p=0.0224). The WSR test on the median estimate for the combined data (all units) is 0.0250, which 

indicates that the Morgantown measurements are higher than the Pittsburgh measurements.
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Table 3: Positive Pressure Test (STP-0120) Statistical Analysis (LabVIEWTM Only)

Unit p-value Median Estimate C.I. or Min, Max

Sperian-Honeywell 0.2500 0.1000 0.100, 0.100

Dräger 1.0000 -0.0125 -0.050,0.000

Avon-ISI NA 0.0000 0.000, 0.000

Interspiro 1.0000 0.0125 0.000, 0.050

Scott NXG 1.0000 0.0125 0.000, 0.050

Scott 2.2 NA 0.0000 0.000, 0.000

Scott 4.5 0.5000 0.0500 -0.050, 0.150

MSA 0.5000 0.0375 0.000, 0.050

Wilcoxon Signed Rank Test 0.0224 0.0250 95% C.I. = 0.000, 0.010

Sign Test (exact Binomial) 0.0654 - -

Kruskal-Wallis Test 0.1102 - -

Out of the 24 difference estimates (Morgantown – Pittsburgh) there were two negative values, 13 zero 

values, and nine positive values suggesting that there is a tendency for higher measurements in 

Morgantown.

Examining each of the eight systems separately, the median estimate of the difference was negative 

(which would indicate higher results for Pittsburgh) for only one of the systems (Dräger), for which two 

of the three data points were zero. The median estimate was zero (indicating no difference between 

Morgantown and Pittsburgh estimates) for two of the systems (Avon-ISI and Scott 2.2) for which all 

three data points were zero. The median estimate of the difference was positive (indicating higher 

results for Morgantown) for five of the systems (Sperian-Honeywell, Interspiro, Scott NXG, Scott 4.5, 

and MSA).

A Kruskal-Wallis test comparing the difference between Morgantown and Pittsburgh indicates there is 

no statistically significant difference among the systems (p=0.1102).
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3.4 Conclusion

To address the need to potentially replace a piece of aging test equipment (Gould RS3200) that can no 

longer be purchased or repaired, NPPTL had a PC based LabVIEWTM program developed. During this 

time, NPPTL also setup a new laboratory in Morgantown, WV. Eight SCBAs were used to conduct a 

correlation study between the LabVIEWTM system and the Gould system, as well as the LabVIEWTM 

systems in Pittsburgh and Morgantown. Statistical analysis of the data indicates that there is no 

statistically significant difference (p=0.2100) in the data comparing the LabVIEWTM system to the Gould 

system in Pittsburgh. Likewise, there was no statistically significant difference (p=0.1102) in the data 

comparing the LabVIEWTM system in Pittsburgh to the LabVIEWTM system in Morgantown

4 REFERENCES

Approval of Respiratory Protective Devices, 42 C.F.R, Part 84

December 7, 2017 NIOSH NPPTL Meeting for All Respirator Manufacturers