Sierra SL-800 User Manual

Instruction Manual

Revision A.2

May 2007

Cal=Trak SL-800 Primary Gas Flow Calibrator

Instruction Manual

Revision A3 June 2008

Worldwide Locations to Serve You

CORPORATE HEADQUARTERS

5 Harris Court, Building L Monterey, CA, 93940 USA

Phone [phone] [phone] Fax [phone]

www.sierrainstruments.com

EUROPE HEADQUARTERS

Bijlmansweid 2, 1934RE Egmond a/d Hoef, The Netherlands

Phone [phone] Fax [phone]

ASIA HEADQUARTERS

Room A618, Tomson Centre

188 Zhang Yang Rd, Pu Dong New District, Shanghai, PR China 200122

Phone + 8621 5879 8521 Fax [phone]

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Table of Contents

Sierra Instruments Contact Information 2
Table of Contents 3

1.0 General Description 5

2.0 Theory of Operation 5

3.0 Cal=Trak Layout 7

4.0 Unpacking Checklist 7

5.0 Warnings 8

6.0 Installation 9

6.1 Attaching and Removing Flow Cells 9

6.2 Connecting the Cal=Trak to a Flow Source 9

6.3 The Cal=Trak Measurement Cycle 9

6.4 Application Precautions 11

6.5 Comparison vs. Calibration, the “4-to-1 rule” 11

7.0 Installation Diagrams and Application Guide 12

7.1 Comparison of Cal=Trak with Piston or Bell Provers 12

7.2 Vacuum Comparison of Cal=Trak with Piston or Bell Provers 13

7.3 Comparison of Cal=Trak with Laminar Flow Element Transfer Standards 14

7.4 Comparison of Cal=Trak with Sonic Nozzle Transfer Standards 14

7.5 Vacuum Comparison of Cal=Trak with Sonic Nozzle Transfer Standards 15

7.6 Calibration of Mass Flow Controllers (MFCs) 15

7.7 Calibration of Mass Flow Meters (MFMs) 16

7.8 Calibration of Rotameters (Variable Area Flow Meters) 16

8.0 Operating Instructions 17

8.1 The Cal=Trak Keypad 18

8.2 How to Use the Cal=Trak Keypad 18

8.3 Factory Default Settings 19

8.4 Taking Readings 19

8.5 Setting User Preferences 20

8.6 Setup Menu 1, Calibration ID #, Gas Constant, Calibration Type 20

8.7 Setup Menu 2, Reading Type, # in Average, Minutes/Reading 21

8.8 Setup Menu 3, Temp. Correction Factor, Temp. & Pressure Formats 21

8.9 Setup Menu 4, Date, Time & Battery Voltage 21

8.10 Setup Menu 5, Date & Time Formats 22

8.11 Setup Menu 6, Leakage & LCF (Leakage Correction Factor) 22

9.0 Battery System 22

9.1 Battery Maintenance and Storage 22

10.0 Maintenance 22

11.0 Quality Assurance 23

11.1 Leak Test Procedure 23

11.2 Calibration 24

11.3 Returning Your Unit for Calibration or Service 25

14.4 Shipment 25

11.5 Replacement Parts & Accessories 25

11.6 Additional Information 26

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12.0 Limited Warranty 27
Appendices
A Cal=Trak Trouble Shooting Guide 28
B Cal=Trak Specifications 31
C Cal=Soft Communication Program 32

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1.0 General Description

The Sierra Cal=Trak SL-800 is the most accurate commercially available gas flow calibrator. Using near-frictionless piston technology, it
combines the accuracy of a primary standard with unequaled speed and convenience.

The Cal=Trak consists of two primary sections. The base houses the main computer, time base and barometric pressure sensors while the
flow cell performs the actual physical measurements using a precision-machined graphite composite piston and borosilicate glass tube. The
flow cell also contains the integrated temperature sensor. The base has 9-pin connector and two guide pins on its upper surface into which
the interchangeable flow cells are installed.

Mass (Standardized) or volumetric flow readings are obtained with the push of a button. The Cal=Trak can be set to take flow readings
manually, one reading at a time, or automatically, in the auto-read mode. The Cal=Trak can be programmed for up to 100 readings in an
averaging sequence. It can be used to measure gas flow rates from most positive pressure sources or under vacuum. Please contact Sierra
Instruments for special precautions before using your Cal=Trak under vacuum.

The Cal=Trak includes a convenient LCD user interface in the base unit. In addition, an RS-232 port for computer interface capability is
provided. An Application program for downloading data from Cal=Trak into Microsoft Excel is on the included CD-ROM. See Appendix
C: Cal=Trak Software Instructions for Data Downloading at the end of this Manual.

2.0 Theory of Operation

The Sierra Cal=Trak SL-800 is a true primary gas standard. The time required for the graphite composite piston to traverse a known
distance through the flow cylinder is precisely measured and an internal computer calculates the flow. The volumetric accuracy of the
instrument is built into its dimensional characteristics. Standardization of the gas flow readings to obtain mass flow is achieved with
precisely calibrated temperature and pressure sensors.

Piston provers like the Cal=Trak are characterized by the most basic of quantities: length and time. As flow is necessarily a derived unit, a
dimensionally characterized system would be as close as possible to direct traceability from national dimensional standards.

An idealized piston prover would consist of a mass-less, friction-less, leakproof, shape-invariant and impermeable piston inserted within the
flow stream and enclosed by a perfect cylinder. The time that the piston takes to move a known distance (which implies a known volume)
then yields the volumetric flow Q as:

π

Q = V / T =

Where:

• V is measured volume

• T = measurement time

• r = radius of cylinder

• h = length (height) of measurement path

Such a device would be as accurate as its physical dimensions and its clock, with almost insignificant drift mechanisms. Although such
idealized devices do not exist, we believe the Cal=Trak offers close to ideal performance (Figure 1).

The Cal=Trak clearance-sealed prover uses a piston and cylinder fitted so closely that the viscosity of the gas under test results in a leakage
small enough to be insignificant. For reasonable leakage rates, such a gap must be approximately 10 microns. As a practical matter, the
piston and cylinder are made of graphite and borosilicate glass because of their low, matched temperature coefficients of expansion and low
friction.

r2 h / T

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Cylinder

Vent

Light

Emitter

Inlet

Inlet Filter

Photodiode
/ Collimator

Bypass Valve

Piston

Inventory Volume

Figure 1 Idealized Automatic Piston Prover

In order to make an intrinsically volumetric device useful for measurement of gases, it is generally necessary to adjust the readings to a
standardized temperature and pressure, yielding mass flow. For this reason, we include temperature and pressure transducers to allow
computation of standard (mass) flow by the internal computer (Figure 2).

Vent

Cylinder

Inlet

Inlet Filter

Light

Emitter

Piston

Absolute

Transducer

Temperature

Transducer

Figure 2 Practical Piston Prover

Photodiode
/ Collimator

Bypass Valve

Inventory Volume

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3.0 Cal=Trak Layout

4.0 Unpacking Checklist

Your Sierra Cal=Trak has been packaged with care and includes all components necessary for complete operation. Please take a moment to
check that you have received the following items. If you believe you have not received a full shipment or if you have any questions, please
contact Sierra immediately.

Your Cal=Trak SL-800 Base Includes

• Cal=Trak SL-800 Electronic Base

• Battery Charger

• Leak Test Cable

• RS-232 Cable

• Instruction Manual

• Certificate of Calibration (behind top cover foam insert)

• Warranty Card (behind top cover foam insert)

• Cal=Soft CD-ROM (Application software for downloading data to your computer and making calibration certificates)

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Each of Your Cal=Trak SL-800 Flow Cells Includes

• Cal=Trak SL-800 Flow Cell

• Leak Test Plug

• Certificate of Calibration (behind top cover foam insert)

• Warranty Card (behind top cover foam insert)

If you purchased your calibrator with the Cal=Trak case, it should look like this when you receive it:

5.0 Warnings

The Sierra Cal=Trak is not rated intrinsically safe and is not for use with explosive gasses or for use in explosive environments.

The Sierra Cal=Trak is designed for use at ambient pressures. This is easiest to obtain by leaving the outlet open to atmospheric
pressure. For vented applications, up to 5 inches of water column (12 mbar or 0.18 PSI) at the outlet fitting maybe used without impact on
measurement accuracy. More than this pressure will add additional uncertainty to the flow readings. Do not use the Cal=Trak with a
differential pressure above 0.35 bar (5 PSI). In other words, the pressure differential across the flow cell must be less than 0.35 bar or the
flow cell may be damaged. Please visit www.sierrainstruments.com for the most current product specifications.

The Sierra Cal=Trak is for use with clean laboratory air or other inert, non-corrosive gases only.

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6.0 Cal=Trak Installation

6.1 Attaching & Removing Flow Cells

The Sierra Cal=Trak accepts interchangeable cells for different flow ranges. If user tries to enter “Run Menu” prior to installing a flow cell,
the unit indicates “No Cell” and returns to the “Main Menu” after a 5 second delay.

Attaching Flow Cells

1. Position the selected flow cell into the electronics base opening with its silver Sierra Instruments label facing you.

2. Locate the guide pins; when the guide pins are engaged, press down firmly.

3. When the power is turned on, the base electronics will sense which cell is installed and display the appropriate units for that cell.

Removing Flow Cells

Grasp the flow cell firmly by the base of the cylinder and lift upward out of the base.

6.2 Connecting the Cal=Trak to a Flow Source

As the accuracy of the Cal=Trak is dependent upon the mechanical set-up (plumbing) of the device under test, it is useful to review the
basic operation of the calibrator prior to plumbing. Always remember the following important guidelines:

1. The accuracy of the Cal=Trak is dependent upon its source being stable. An unstable flow source may produce inconsistent

readings.

2. Sierra Instruments’ Cal=Trak is designed to be used at ambient pressures. This is easily accomplished by leaving the outlet of the

flow cell open to atmosphere for positive pressure installations or the inlet open to atmosphere for vacuum installations. If a vent
hose is required on the outlet fitting, a maximum pressure of 5 inches water column (0.18 psi or 12 mbar) above ambient is
acceptable. Exhaust pressure of more than this amount will add additional uncertainty to the flow measurements of Cal=Trak.
One way to reduce exhaust pressure is to increase the diameter of the vent line. Do not subject the Cal=Trak to a differential
pressure above 0.35 bar (5 PSI). In other words, the pressure drop across the Cal=Trak calibrator must not exceed 0.35 bar (5
PSI) or damage may occur. In vacuum scenarios, make certain that the pressure drawn across the Cal=Trak does not exceed 0.35
bar (5 PSI).

3. Flow direction is indicated by the arrow on the top of the flow cell. To use a pressure flow source, connect to the inlet fitting, or

to use a vacuum flow source, connect to the outlet fitting.

6.3 The Cal=Trak Measurement Cycle

Operation of a Cal=Trak is extraordinarily simple, and little training is required. However, any measurement interacts with the device being
calibrated to some degree. Often, these interactions are negligible. However, sometimes device interactions can seriously affect
measurement accuracy. Here we will explain what happens during a Cal=Trak measurement to aid in installing and using the instrument
appropriately.

In its inactive state, the Cal=Trak will, like any device, exhibit a constant insertion pressure drop. At all but the highest flows, the pressure
drop is very small. In the inactive state, gas flows from the inlet to the outlet through the bypass valve (Figure 3
cycle begins, the bypass valve closes, and the gas is directed into the cylinder, effectively inserting the piston in series with the gas flow,
allowing measurement. Timing commences after the piston has accelerated to the flow stream’s speed. At the end of the timed cycle, the
valve opens and the piston falls to its inactive position at the bottom of the cylinder.

). When a measurement

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Piston

Outlet

Bypass Valve

Inle t

Figure 3 Basic Piston Prover

In real-world applications, there are significant dynamics to consider. At the beginning of a cycle, pressure rises rapidly until the piston
accelerates to the speed of the flow stream. Figure 4

is an illustration of a typical Cal=Trak’s internal pressure during a measurement cycle.
A near-maximum flow rate is illustrated to accentuate the pressure variations. The initial pressure pulse, lasting some tens of milliseconds,
reaches a peak of about 0.5 kPa, or 0.5% of its working, near-atmospheric pressure. The pressure settles out to about 0.1 kPa (0.1% of
working pressure) during the timed period. This pressure represents the added pressure due to the weight of the piston. Very small
oscillations continue due to the piston’s under damped nature.

0.8

Initial Pressure Pulse

0.6

0.4

0.2

0

0 100 200 300 400 500 600 700 800 900 1000

-0.2

Intracell Pressure (kPa)

-0.4

M illiseconds

Timing
Begins

Timing
Ends

-0.6

-0.8

Figure 4 Cal=Trak Internal Pressure

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6.4 Application Precautions

Although the Cal=Trak’s dynamic pressure effects are very small, in some circumstances they may affect the measurement or interact with
the device under test. For the above reasons, certain precautions should be observed when using a Cal=Trak.

Initial Pressure Pulse

The initial pressure pulse is small, about 1% of an atmosphere or less. However, even so small an increase may affect some very sensitive
transducers for several seconds. Two examples of this are the resonant transducers used in LFE systems such as the DH Instruments
Molbloc or capillary-based systems. For this reason, the LFE instrument may not be accurate for a number of seconds after the start and the
end of a Cal=Trak measurement cycle. When calibrating such systems, a stable flow source should be used and the LFE read before and
after the Cal=Trak cycle.

Intra-Cycle Pressure Change

After the initial brief pressure pulse, the change in insertion pressure is typically 0.1% of an atmosphere (~0.1 kPa or 1 cm water column).
This is usually insignificant. For example, flow from a 100 kPa gauge pressure (15 psi) source will change by 0.1%. However, very low
pressure sources will show larger flow change during a Cal=Trak cycle and may require compensating calculations to achieve Cal=Trak’s
best applied accuracy.

Inventory (Dead) Volume

Inventory volume consists of all the space contained between the flow source’s point of restriction and the timed portion of the cylinder.
This includes tubing, empty space within the Cal=Trak base, the lower portion of the measuring cylinder and any other space contained
within the test setup.

It is important to keep inventory volume to a minimum. Excess inventory volume amplifies
the Cal=Trak cell. In extreme cases, the excess volume also prevents gas pressure from accelerating the piston properly, causing significant
errors in readings. Ideally, the volume contained between the cell and the flow source should be on the order shown in Table 1
shows the volume as an equivalent length of tubing.

the effects of minute pressure variations within

, which also

Table 1 Recommended Maximum External Volume and Tubing Lengths

Recommended Max.

Cell Size

Small (SL-500-10) 9 1.2 (47.2”) 0.3 (11.8”) N/A

Medium (SL-500-24) 46 6.5 (256”) 1.6 (63.0”) 0.7 (27.6”)

Large (SL-500-44) 118 16.7 (658”) 4.2 (165”) 1.9 (74.8”)

Volume (cc)

Recommended Maximum Length—meters (inches)

3mm ID (1/8“) 6mm ID (1/4“) 9mm ID (3/8“)

6.5 Comparison vs. Calibration

Calibration consists of comparing an instrument with one of significantly greater accuracy (ideally, at least four times the accuracy of the
device under test--the “4 to 1 rule” widely accepted by industry). We use the term “comparison” in most of the following applications
because, depending upon their respective accuracies, either device can be calibrating (or simply compared with) the other.

For example, a 0.2% LFE can calibrate a 1% mass flow controller, while a 0.15% Cal=Trak can calibrate a 0.6% LFE. On the other hand, a

0.15% lab prover cannot calibrate a 0.15% Cal=Trak to its rated accuracy (or vice-versa). One can calibrate the other to only 0.3% with
great certainty, so we simply call it a comparison.

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7.0 Installation Diagrams and Application Guide

A

7.1 Comparison of Cal=Trak with Piston or Bell Provers

Piston or bell provers have a much longer measurement time than the Cal=Trak. For this reason, it is possible to compare them
simultaneously, but certain precautions must be observed. When the Cal=Trak begins its cycle, the piston’s weight causes the internal
pressure to rise by about 0.001 atmospheres (~0.1 kPa). If a simple pressure regulator feeds the test chain, we are simply using the
resistance of the entire flow chain to set our flow rate. The rate will then change significantly when the Cal=Trak is in its measurement
cycle. This will cause the actual flow measured during the Cal=Trak cycles to be less than the average flow seen by the piston or bell
prover.

To render this effect insignificant, the flow must not be affected significantly by the Cal=Trak’s cyclic pressure increase. This can be
achieved by use of a sonic nozzle as the stable flow source, or by feeding a fixed restrictor with a precisely regulated pressure of more than
200 kPa, as is used in factory calibration of the Cal=Trak. Note that at 200 kPa (30 PSI), the dynamic flow decrease of a simple restrictor
caused by the piston’s weight will be about 0.05%. In certain circumstances, the sonic nozzle or porous plug flow generator may be
replaced with a mass flow controller (MFC) specifically tailored to this task. An example is the Sierra Model C100L-10, -24 and -44, each
specifically built to provide a stable flow source for the Cal=Trak calibrator.

For this type of calibration, we can use the setup shown in Figure 5
a properly sized flow restrictor. A piston or bell prover cycle is instituted. The Cal=Trak and the prover can then be alternately measured
using the fixed flow source.

. The adjustable regulator is used to set the flow rate within the range of

Gas
Supply

An alternative approach can be used with piston provers, as shown in Figure 6.
a Cal=Trak. The Cal=Trak is then started in a cyclical mode, averaging its flow. Before the prover ends its cycle, the Cal=Trak is stopped
and the average flow read.

The Cal=Trak can be set for sufficient cycles in its average to allow interruption by the “stop” button, or smaller averages, such as 5 or 10
readings, can be taken during the prover cycle. It should be noted that the periodic pressure pulses might cause oscillations in bell provers,
reducing the bell prover’s accuracy somewhat.

Fixed
Regulator

djustable

Regulator

Stable Pressure
> 200 kPa

Figure 5 Setup for Piston or Bell Provers

Sonic
Nozzle

OR Porous Plug

DryCal

Cal=Trak

Piston or
Bell Prover

A cycle is initiated on the prover, which is much slower than

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