RH CGS-240 User manual

CGS-240
RH Systems, LLC
1225 W Houston Ave.,
Gilbert AZ, 85233
Manual

Introduction
CGS-240 Manual 6/15/2021
Page 2 of 148
TABLE OF CONTENTS
Introduction.............................................................................................................................. 4
1.1 Background of Humidity Generation .............................................................................................................4
1.2 Scope .............................................................................................................................................................4
Theory of operation ................................................................................................................. 5
2.1 Two-pressure principle ..................................................................................................................................5
2.2 Combined two-pressure and two-temperature principle .............................................................................6
2.3 Common Defining Equations .........................................................................................................................6
2.4 Humidity Equations .....................................................................................................................................10
Installation.............................................................................................................................. 13
3.1 Facility Requirements ..................................................................................................................................13
3.2 Utility Connections ......................................................................................................................................14
3.3 Initial Preparation ........................................................................................................................................17
Operation ............................................................................................................................... 22
4.1 Introduction to Software .............................................................................................................................23
4.2 Connection Window ....................................................................................................................................24
4.3 Enter Set Point.............................................................................................................................................25
4.4 Selecting Control mode and initiating Generate .........................................................................................26
4.5 Viewing Data Numerically and Graphically..................................................................................................29
4.6 Change Units................................................................................................................................................31
4.7 Connection of Other Instruments................................................................................................................31
4.8 Data Logging ................................................................................................................................................32
4.9 System Settings............................................................................................................................................33
4.10 Chamber ......................................................................................................................................................34
4.11 Door .............................................................................................................................................................35
Calibration.............................................................................................................................. 36
5.1 Pressure Calibration.....................................................................................................................................36

Introduction
CGS-240 Manual 6/15/2021
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5.2 Temperature Calibration .............................................................................................................................46
Subsystems............................................................................................................................. 53
6.1 Electrical System..........................................................................................................................................53
6.2 Pneumatic System .......................................................................................................................................58
6.3 Fluid System.................................................................................................................................................62
6.4 Refrigeration System ...................................................................................................................................65
6.5 Heaters.........................................................................................................................................................68
6.6 Connections to the ECB ...............................................................................................................................71
6.7 Temperature Measurements.......................................................................................................................75
Troubleshoot/Maintenance................................................................................................... 76
7.1 Preventative Maintenance ..........................................................................................................................76
7.2 Troubleshooting...........................................................................................................................................82
Illustrated Parts Breakdown................................................................................................... 90
8.1 Parts List.......................................................................................................................................................90
8.2 Illustrations ..................................................................................................................................................97
Drawings............................................................................................................................... 119
RHS Plateau Software ....................................................................................................... 134
10.1 Introduction...............................................................................................................................................134
10.2 Sequence of Events....................................................................................................................................136
10.3 Data File Selection .....................................................................................................................................139
10.4 Evaluating for Plateaus ..............................................................................................................................141
10.5 Selecting a Manual Reference ...................................................................................................................143
10.6 Calculating Calibration Coefficients...........................................................................................................144
10.7 Plotting Residuals ......................................................................................................................................146
10.8 Export Data ................................................................................................................................................147
Document History............................................................................................................. 148

Introduction
CGS-240 Manual 6/15/2021
Page 4 of 148
INTRODUCTION
The RH Systems CGS-240 Humidity Generator is a system capable of continuous, high-accuracy humidity
generation over a wide range of humidity, temperature, and flow rates. The CGS-240 design is an RHS hybrid two-
pressure two-temperature system based on the fundamental two-pressure principle originally developed by NIST.
The basis of this principle and its original development are discussed below.
1.1 BACKGROUND OF HUMIDITY GENERATION
In 1948 at the U.S. National Bureau of Standards (now the National Institute of Standards and Technology), E.R.
Weaver and R. Riley developed a “pressure method” for the generation and control of humidity. Their method,
termed the two-pressure principle, was derived from measurements of temperature and pressure rather than
requiring measurements of water vapor.
Using their technique, air or some other gas was saturated with water vapor at high pressure and then expanded
to a lower pressure. When saturation and expansion were performed under constant-temperature conditions, the
resulting relative humidity of the gas was simply the ratio of the lower pressure to the higher pressure (or at least
very nearly).
Their equipment was designed for low rates of gas flow and was used under ambient temperature conditions.
Their saturator was a small cylinder containing water and filled with fragments of pumice or stream-washed gravel
through which the gas could be bubbled under pressure. This device was developed primarily for the calibration of
electrically conductive hygroscopic films used in the measurement of water vapor in gases.
In 1951, also at the National Bureau of Standards, the two-pressure principle was the foundation on which A.
Wexler and R.D. Daniels developed a new “pressure–humidity apparatus” with higher air-flow capability. Another
significant improvement was the incorporation of temperature control. Developed primarily for hygrometer
research and calibration, it was capable of producing atmospheres of known relative humidity from 10 %RH to 98
%RH over a fairly wide temperature range –40°C to +40 °C.
Wexler also designed and constructed a low-humidity generator based on a method termed the two-temperature
principle. With the two-temperature principle, a stream of air or other gas is saturated with water vapor at a given
temperature; then its temperature is raised to a specified higher value.
1.2 SCOPE
The CGS-240 Humidity Generator is a portable, self-contained system which produces stable atmospheres of
known humidity and temperature using the two-temperature, two-pressure saturated vapor stream principle. Its
capability and intended purpose is to provide accurate humidity and temperature for the calibration of humidity
sensors, hygrothermographs, chilled mirror hygrometers, and other environmental measuring devices.

Theory of operation
CGS-240 Manual 6/15/2021
Page 5 of 148
THEORY OF OPERATION
2.1 TWO-PRESSURE PRINCIPLE
In an ideal two-pressure system, a stream of gas at an elevated pressure is saturated with respect to the liquid or
solid phase of water and then expanded isothermally to a lower pressure. Measurements of the pressure and
temperature of the gas stream, both at saturation and after expansion, are all that is required to determine the
resulting humidity content of the expanded gas stream. The two-pressure system is shown in Figure 1.
Figure 1—Simplified schematic diagram of the two-pressure principle where Tsis saturator temperature, Tcis
chamber temperature, and Ts= Tc.
A two-pressure generator is commonly used in the generation of a range of relative humidity values at fixed
temperatures. The saturator and chamber share a common fluid bath temperature and are, ideally, in thermal
equilibrium with each other. In this case, where saturator temperature, Ts, and chamber temperature, Tc, are of
nearly the same value, the generated relative humidity may be approximated by the ratio of the measured
saturated gas-stream pressure (saturator pressure) to the measured chamber pressure by using the simplified
expression
RH = 
P
P
c
s
100
where Pcis the absolute chamber pressure
Psis the absolute saturation pressure.
Please note that the above expression ignores the use of enhancement factors which account for non-ideal
properties of the air / water-vapor mixture, and is therefore only an approximation. More exacting equations
which include enhancement factors are used internally within the system.
Saturation
Pressure, Ps
Chamber
Pressure, Pc
Expansion
Valve
Inlet
Valve
Exhaust
Valve
Saturator
Chamber
Constant Temperature Bath, Ts= Tc
High
Pressure
Source
Atmosphere or
Vacuum Source