Download Humidty Transmitter Manual

HYGRODYNAMICS
HUMIDITY
TRANSDUCER/TRANSMITTER
CATALOG NO. 7012, 7012D
7012W, 7012DW
SERIAL NO. 926-1 AND UP
NEWPORT SCIENTIFIC, INC.
8246-E SANDY COURT
JESSUP, MARYLAND 20794
PHONE: (301) 498-6700
FAX: (301) 490-2313
DECEMBER1990
TABLE OF CONTENTS
I.
INTRODUCTION
Transducers For Special Applications
Duct Mounting
Weatherproofing
Custom Range And Output Transducers
II.
INSTALLATION
A. Selecting a Suitable Location
C.
Circuit Protection
D.
Mounting
E.
Connections
Cable Assembly
Input/Output Connections
1
1
1
2
2
2
2
3
3
4
4
4
III.
PRINCIPLES OF OPERATION
6
IV.
PERFORMANCE CHARACTERISTICS AND SPECIFICATIONS
6
Specifications
V.
OPERATION
8
Humidity and Temperature Operating Limits
VI.
VII.
8
CALIBRATION PROCEDURES
8
Initial Adjustment
8
PRECAUTIONS, LIMITATIONS AND HAZARDS
A.
B.
C.
D.
VIII.
7
Warnings
Precautions
Limitations
Humidity And Temperature Operating Limits
Pressure And Vacuum Operating Limits
Gas Velocity Operating Limits
Contaminants
Physical Contaminants
Chemical Contaminants
10
10
10
10
10
11
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12
MAINTENANCE
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A.
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Calibration Service
FIGURES
1.
2.
3.
4.
Transducer/Transmitter
7012 and 7012D Transducer Mounting Dimensions
Cable Assembly Detail
4
Input/Output Circuit Configurations
1
3
5
I.
INTRODUCTION
The HYGRODYNAMICS® Transducer/Transmitter, Figure 1, consists of a multi-element
humidity sensor and transmitter mounted in a compact metal case. The transmitter circuit
provides a current or voltage output signal proportional to relative humidity when the
transducer is connected to a DC power supply.
The transducer humidity sensor is made up of a number of HYGROSENSOR ® elements
in an electrical network which enables measurement over a wide range of relative
humidity. Each sensor element consists of a plastic rod supporting a dual winding of
precious metal wire coated with a moisture-sensitive compound, and enclosed in a
perforated, plastic jacket. The sensor elements are mounted on a common base and
protected by a ventilated cover.
TRANSDUCERS FOR SPECIAL APPLICATIONS
Duct Mounting
Transducers for duct mounting applications, Figure 1B, are identified by suffix D to the
catalog number. These transducers are mounted on a 5-1/8 inch diameter aluminum
flange with six (6) mounting holes.
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Figure 1. Transducer/Transmitter
2
Weatherproofing
Weatherproof transducers, identified by suffix W to the catalog number, are fabricated
with a protective weatherproof covering over the element winding for protection against
condensation. For outdoor applications, these transducers should be mounted in a
weather shelter (available from Newport Scientific, Inc.). Refer to "Limitations" paragraph
in Section VII. for operating limits.
II. INSTALLATION
A.
SELECTING A SUITABLE LOCATION
Humidity measurement is complicated by the effect of variables such as temperature,
pressure, and the presence of hygroscopic materials. The humidity sensor indicates the
moisture conditions of the environment immediately surrounding the sensor. Therefore,
the sensor should be located where the environment is representative of the conditions to
be measured, or where the difference between the point of measurement and the point of
use of a created condition is known and recorded for conversion purposes. Avoid
installation in stagnant air or near a radiant of conductive heating or cooling surface. In
some applications, a small electric fan may be used to draw air over the sensor to provide
a representative air sample and to reduce the risk of condensation from warm, moist air
flowing over a cold sensor. Look for the presence of hygroscopic material (wood, textile,
etc.) near the proposed mounting location which, in semi-stagnant air, could significantly
influence the immediate environment.
B.
PROTECTION OF SENSOR
If the atmosphere in which a sensor is to be used is known to be very dirty or contains
conductive materials, such as graphite or sooty particles, the sensor should be protected.
The type and size of contaminant will govern the type of protection required. A mesh
screen may be used for large particles, while facial tissue, nylon, or moisture-pervious
cellophane may be used for extremely dirty or oily atmospheres. The protective
coverings will decrease the speed of response; however, the down-stream side of the
protective covering can be perforated, the number and size of perforations being
increased until optimum response and protection are achieved.
WARNING
THE SENSITIVE SURFACE OF THE SENSOR IS
EXPOSED TO THE ATMOSPHERE BEING SENSED
AND MAY NOT MEET CERTAIN
EXPLOSION-PROOF REQUIREMENTS.
HOWEVER, THE ELEMENT IS SPARKLESS,
DRAWS LITTLE CURRENT (100 MICROAMPERES
MAXIMUM) AND DOES NOT GENERATE HEAT.
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C.
CIRCUIT PROTECTION
When input voltages above +18 VDC are to be used, heat may be generated by the circuit
in the base of the transducer. Ensure that the transducer is mounted on a
heat-dissipating surface or on a heat-sink to maintain operating temperatures below 51
C. (125 F.) to protect the circuit and to minimize psychrometric error.
PRECAUTION
TEMPERATURES ABOVE 51 C. (125 F.) WILL
DAMAGE THE TRANSDUCER.
D.
MOUNTING
The transducer is not position sensitive and may be oriented in any position. The
transducer should be mounted on a heat sink if input power exceeds +18 VDC. Ensure
that the flat side of the base makes good contact with the heat sink so that heat generated
will be readily dissipated. Do not obstruct the adjustment screw at the side of the base,
Figure 2A.
PRECAUTION
DO NOT USE ANY OF THE SCREWS ON THE CASE
FOR MOUNTING PURPOSES.
The 7012D Transducer has a permanently attached 5-1/8 inch diameter by 1/16 inch
thick aluminum plate, Figure 1B, for duct or through-wall mounting. This transducer
requires a 2-7/8 inch minimum diameter hole through the mounting surface, Figure 2B.
Six (6) 1/4 inch diameter (No. 25 drill) mounting holes are spaced 30 degrees apart on
4-1/4 inch diameter centers around the mounting plate, Figure 2B.
NOTE: ALL DIMENSIONS IN INCHES
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Figure 2. 7012 And 7012D Transducer Mounting Dimensions
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E.
CONNECTIONS
The measuring circuit is contained in the base of the transducer assembly with power
input and signal output connections through a common 6-terminal male MS connector. A
6-pin female connector (MS 3106A-14-6S) and cable clamp (9767-14-6) are supplied
with the transducer. The connecting cable and other external circuit components
required, Figure 4, must be supplied by the user.
Cable Assembly
1.
Connect a 6-conductor cable (Belden No. 8446 or equivalent) to the 6-pin
connector supplied as indicated in Figure 3. Solder all connections. Install cable
clamp.
2.
Terminate leads at other end of cable to mate with the input power source and with
the voltage or current read-out device as described in the connection diagrams,
Figure 4.
Input/Output Connections
3.
Connect terminals C and D to a +8 to +32 VDC power source as follows:
- terminal C to the negative connection.
- terminal D to the positive connection.
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The transducer is provided with a safeguard against damage due to inadvertent
input voltage polarity reversal; however, some custom models may not include this
feature and precautions must be taken to prevent polarity reversal.
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Figure 4. Input/Output Circuit Configurations
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4.
Depending on the output desired, connect conductors A, B, E, or F according to
the circuit configurations shown in Figure 4. Unused terminals should be cut or insulated
and taped back.
External circuit components shown are NOT supplied with the
transducer.
NOTE
THESE CONNECTION DIAGRAMS APPLY ONLY TO SERIAL NO. 926-1 AND
UP TRANSDUCERS.
III.
PRINCIPLES OF OPERATION
Operation of the sensor is based upon the ability of a hygroscopic film to change its
electrical resistance significantly and rapidly with small changes in relative humidity.
Each of eight (8) cells in the sensor covers a narrow span of relative humidity overlapped
by the span of the adjacent cell. These cells, linked with precision resistors in a ladder
network, comprise the sensor which is designed to cover the full span of relative humidity.
The transducer sensor resistance is governed by the hygroscopic coating of lithium
chloride and/or lithium bromide.
The circuit in the base of the transducer consists of an input voltage regulator, a
transistor, a transistor oscillator, a temperature compensating circuit, and a relative
humidity measuring network. The oscillator provides about 400 Hz through a transformer
to the sensor. The output of the sensor is rectified by a full-wave bridge and combined
with a temperature signal generated by a precision thermistor located in the humidity
sensor compartment. This temperature signal compensates for the temperature effect on
the sensor output. The rectified and temperature-compensated signal is then filtered and
is converted into a current or voltage output signal for a readout unit.
IV.
PERFORMANCE CHARACTERISTICS AND SPECIFICATIONS
The voltage and/or current output signal of the Transducer/Transmitter is directly
proportional to relative humidity within the ranges listed in the specifications.
The transducer has calibration capability by using an internally stored set-plug and an
adjustable calibration screw.
Standard transducer specifications are listed below. Refer to the supplemental
specification sheet for performance characteristics of custom-made transducers.
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A.
SPECIFICATIONS
HUMIDITY RANGE:
ACCURACY
10 - 99% RH, limited to 38 C. dewpoint and
43 C. dry-bulb (100 F. dew-point and 110 F.
dry-bulb).
+3% between 4.5 and 49 C. (40 and 120F.).
INPUT VOLTAGE:
+8 TO +32 VDC.
CURRENT:
30 milliamperes at any voltage from
OUTPUT VOLTAGE:
0 to 5 volts DC, adjustable, proportional to
0-100% nominal output. Allowable load - 200K
ohms or higher resistance across output
terminals.
CURRENT: 0 TO 150 microamperes, nominal, proportional to 0 - 100% RH.
Allowable load - up to 1000 ohms.
VOLTAGE AND CURRENT:
Simultaneous output permissible if maximum
voltage output at maximum RH exceeds to 0 to
2 volt range.
OUTPUT RIPPLE*:
Approximately 0.5% at approximately 800 Hz.
ELECTRICAL PROTECTION:
Against accidental input voltage polarity
reversal.
BODY SIZE:
5.7 by 5.7 by 11.5 cm (2 by 2 by 4.5 inches);
13.3 cm (5.25 inches) long overall.
BULK:
312 cc (19 cubic inches).
FINISH:
Gold anodized aluminum case.
WEIGHT:
60 grams net; 0.8 kilogram shipping (10 ounces
net; 2 lbs shipping).
MOUNTING ORIENTATION:
Any position.
*If the transducer is used in connection with a high-speed, sampling type readout,
additional filtering may be required to reduce ripple. Contact Newport Scientific, Inc.
(NSI).
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V. OPERATION
The voltage and/or current output signals are proportional to relative humidity. For
example, if the receiver has a 0 to 100 linear scale, the scale indication will correspond
directly to the percent of relative humidity being sensed. If the receiver has a 0 to 5 linear
scale and the transducer has a 0 to 5 VDC output, the indication can be converted to
percent relative humidity by multiplying the scale indication by 20.
1.
Perform the calibration procedures in Section VI. before putting the transducer into
service.
2.
Apply power (+8 to +32 VDC) to the transducer. The readout unit should indicate
the percent of relative humidity to which the sensor is exposed.
PRECAUTION
TEMPERATURES ABOVE 51 C. (125 F.) WILL
DAMAGE THE TRANSDUCER.
A.
HUMIDITY AND TEMPERATURE OPERATING LIMITS
From 4.5 to 43 C.(40 to 110 F.) - the transducer may be used in atmospheres up to
near saturation, provided condensation does not occur.
From 43 to 49 C.(110 F.) - the transducer may be exposed to this range, provided
dew-point temperature does not exceed 38 C. (100 F.).
Above 49 C. 120 F.) - the transducer should not be exposed to temperatures
exceeding 51.5 C.(125 F.). If the air or gas has a low absolute humidity, precooling to
temperatures below 49 C. (120 F.) may enable measurements.
Below 4.5 C.(40 F.) - the transducer may be exposed to lower dry-bulb temperatures;
however, the output signal may not be directly proportional to relative humidity and the
transducer may become inoperative near -17.8 C.(0 F.).
Below 4.5 C.(40 F.) or above 49 C.(120 F.) - to operate the transducer in these
ranges, consult NSI.
VI. CALIBRATION PROCEDURES
A.
INITIAL ADJUSTMENT
After initial installation, ensure that the output signal matches the input of the readout
receiver and then adjust for full scale deflection by performing the following adjustment
procedure for the type of output selected. Check this adjustment periodically or when
changing output signal or range.
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1.
Remove the four (4) sheet metal screws on the sides of the case and remove the
vented cover. Note that the sensor assembly consist of eight (8) sensor elements and
that each element and its location are color-coded in a clockwise direction as follows:
brown, red, orange, yellow, green, blue, violet, and gray. The center unit, similar in
appearance except that it is potted, is a resistance set-plug. The center socket serves
only as a holder for the set-plug and is inoperative.
2.
Replace the gray color-coded sensor with the set-plug stored in the center socket.
Insert the set-plug into the socket oriented such that the color-coded patch on the
plug is pointing toward the corner of the case. All other sensors may be left in
place. Perform either step 3, 4 or 5, depending upon the type of output selected.
For Millivolt Input Receiver (Figure 4A)
3.
Connect a 1000 ohm potentiometer as shown in Figure 4A to drive a receiver with
millivolt input. Adjust this potentiometer until full scale deflection is obtained on the
readout receiver. Go to step 6.
For Voltage Input Receiver (Figures 4B and 4C)
4.
Remove the 6-32 screw located at the side of the base or below the nameplate to
gain access to the adjustment screw, Figure 2. Insert a small screwdriver through
the adjustment screw port and, while observing the readout receiver, turn the
adjustment screw for full scale deflection. This corresponds to a nominal 100% RH
when the transducer is connected as shown in Figures 4B and 4C. Replace the
6-32 screw to cover the adjustment screw port. Go to step 6.
For Current Input Receiver (Figure 4D)
5.
Shunt the readout receiver with a variable resistor as shown in Figure 4D. The
current output of the transducer is fixed a approximately 150 microamperes
between pins B and E for a nominal 100% RH indication and is not adjustable
internally. Therefore, any current device can be operated on this output as long as
the maximum current does not exceed 150 microamperes. When less current is
required for the receiver, the current can be reduced by variable shunting resistor
as long as the combined receiver and shunt resistance does not exceed 1000
ohms. If the combined resistance is less than 1000 ohms, include a series resistor
to increase the resistance to 1000 ohms +10%.
6.
Remove the set-plug from the gray socket. Reinsert set-plug into the center
socket.
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7.
Insert the gray color-coded cell into its socket, making sure that the color-code
patch on the cell faces the corresponding color mark on the base near its socket.
8.
Replace the vented cover and secure in place with the four mounting screws.
VII. PRECAUTION, LIMITATIONS AND HAZARDS
A.
WARNINGS
The sensitive surface of the humidity sensor is exposed and may not meet certain
explosion proof requirements. However, the sensor element is sparkless, draws little
current (maximum 100 microamperes), and does not generate heat.
B.
PRECAUTIONS
Do not use any of the screws on the transducer case for mounting purposes, not drill into
the side of the case. Although the operation of the individual sensing elements is
resistive, NEVER apply DC voltage nor test the sensor with a DC volt-ohmmeter; to do so
will damage the sensor permanently. Temperatures above 51 C.(125 F.) will damage
the transducer. When the transducer is operated with more than +18 VDC input, install
transducer on a heat sink to dissipate heat and maintain operating temperatures below
51 C.(125  F.).
C.
LIMITATIONS
The sensor calibration can be altered by changes in the concentration of the hygroscopic
salt, by inserting an individual sensing element into the wrong socket, or by certain
contaminants. Certain conditions with regard to sensor exposure must be taken into
consideration when selecting mounting and operating conditions before installation as
indicated in the following paragraphs.
Humidity and Temperature Operating Limits
From 4.5 to 43 C.(40 to 110 F.) - the transducer may be used in atmospheres up to
near saturation, provided condensation does not occur.
From 43 to 49 C.(110 to 120 F.) - the transducer may be exposed to this range,
provided dew-point temperature does not exceed 38 C.(100 F.).
Above 49 C.(120 F.) - the transducer should not be exposed to temperatures
exceeding 51.5 C.(125 F.). If the air or gas has a low absolute humidity, precooling to
temperatures below 49C. (120 F.) may enable measurements. Facilities for tempering
air under these conditions are available from NSI.
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Below 4.5 C.(40 F.) - the transducer may be exposed to lower drybulb temperatures;
however, the output signal may not be directly proportional to relative humidity and the
transducer may become inoperative near -17.8 C.(0 F.).
Below 4.5 C.(40 F.) or above 49 C.(120 F.) - to operate the transducer in these
ranges, consult NSI.
Pressure And Vacuum Operating Limits
Sensors have been successfully used at 10,000 psig, and have withstood exposure to
vacuum of less than 1 mm Hg (and for brief periods as low as 0.001 mm Hg) without
permanent loss of calibration. Sensors measure humidity at the pressure of the system
independent of the total pressure.
Gas Velocity Operating Limits
Sensors have successfully withstood several hundred mile per hour velocities. However,
in high-velocity gas streams, a deflection shield is recommended as protection against
damage from airborne particles.
D.
CONTAMINANTS
The contaminants listed in the following paragraphs affect the calibration and response of
the sensor. The change in calibration or response is on a time-and-concentrationof-contaminant exposure basis, but periodic calibration verification (a service offered by
NSI) may provide months of service even in contaminating atmospheres.
Physical Contaminants
Physical contaminants such as dust, soot, and oil which may be deposited on the sensor
surface do not affect calibration. However, dust is hygroscopic and slows down response
time and oil forms an insulating film (to water vapor) rendering the sensor inactive.
Conductive physical contamination results from deposition of electrolytic particles such
as metallic dust or salts which change the sensor conductivity and calibration.
Protection against physical contaminants consists of prefiltering the air that passes over
the sensor, or covering the vented cover with a mesh screen for large particles or
moisture pervious cellophane, nylon, or paper tissue for finer particles or oil laden
atmospheres.
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Chemical Contaminants
Chemical contaminants cause a permanent shift in calibration. The hygroscopic salt
concentration of the sensor can be changed by exposure to any material or chemical
vapor that will react with the salt. These corrosive chemicals include: acid vapors,
mercury vapor, unstable hydrocarbons such as ketones and halogen gases, sulfur
compounds such as hydrogen sulfide, and sulfur dioxide, etc.
Temporary poisoning of the sensor can result from exposure to polar vapors wherein the
conductivity of the salt is affected by the material in a manner similar to the effect of water
vapor. Normally these materials are volatile and sensor response returns to normal after
removal from the contaminated atmosphere. Included in this class of contaminants are:
ammonia, amines, alcohols, glycols, and glycerols.
VII. MAINTENANCE
The transducer is part of a high precision measuring system and MUST be treated with
care during installation and use. Failure to observe the following instructions may result in
damage to the transducer.
A small accumulation of lint or dust may collect on the sensors if the transducer is used
continually in an exposed location. This accumulation will not seriously affect sensor
calibration and no attempt should be made to remove this coating as damage to the
sensor may result.
The transducer sensor is a composite of individual plug-in cells. These plug-in cells
should not be removed except to clean the mounting base. If cells must be removed, the
color code and orientation of the mark should be noted. If any cells are omitted or
inserted in the wrong socket, the humidity output signal will be erroneous.
PRECAUTION
NEVER APPLY DC VOLTAGE OR TEST THE
SENSOR ELEMENTS WITH A DC
VOLT-OHMMETER.
A.
CALIBRATION SERVICE
A periodic calibration check should be made every 6 months to 1 year. Contact NSI for
calibration service.
Use of a spare transducer is the most practical means of checking calibration in the field
by comparing readings periodically.
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