COHU 2740 SERIES User manual

Phone: [phone] www.cohu-cameras.com
Cohu Electronics • 12367 Crosthwaite Circle • Poway CA • 92064
Fax: [phone] [email protected]
2740 SERIES
ENVIRONMENTAL CAMERA
INSTALLATION AND OPERATION MANUAL
Technical Manual 6X-1048B
May 10, 2011
Figure 1. Low Light Level Environmental Camera
Shown with optional sun shield

26X-1048B
2740 CAMERA INSTALLATION AND OPERATION
LIST OF
SECTIONS
LIST OF
FIGURES
LIST OF
TABLES
TABLE TITLE PAGE
1 Specifications 4
2 Items Supplied 6
3 Rear Panel Connector and Mating Cable Plug 7
4 Pin F unctions, Rear P anel Connector 11
FIGURE TITLE PAGE
1 Low Light Level Environmental Camera 1
2 Sensor Wavelength Response Characteristics 3
3 Model Number Interpretation Diagrams 5
4 Dimensions, Model 2740Camera 8
5 Typical Interconnection Cable 9
6 Rear Panel Features (Basic Camera) 10
7 Connector Pin Orientation 10
8 Rear P anel Features (Optioned Camera) 11
9 Humidity Indicators 12
SECTION TITLE PAGE
1.0 GENERAL DESCRIPTION 3
1.1 Electrical Characteristics 3
1.1.1 Sensor Characteristics 5
1.2 Mechanical Characteristics 5
2.0 INSTALLATION 6
2.1 Unpacking and Receiving Inspection 6
2.2 Static Discharge Protection 6
2.3 Equipment Supplied 7
2.4 Equipment Required but Not Supplied 7
2.5 Cabling Requirements 7
2.6 Power Requirements 7
2.7 Mounting Requirements 7
2.8 Line Lock Operation 8
2.9 Installation Procedure 8
2.9.1 IDGenerator Messages (Option) 8
2.9.2 Rear Panel Features 10
2.10 Front Window Features 13
2.11 Preparation for Shipment and Storage 13
3.0 OPERATION 13

3
6X-1048B
2740 CAMERA
INSTALLATION AND OPERATION
1.0 GENERAL DESCRIPTION
This introduction briefly describes overall
characteristics of the Model 2740 monochrome
Camera (figure 1) related to its installation and
operation.
1.1 Electrical Characteristics
The 2740 camera provides a highly sensitive
interline transfer CCD Camera in a pressurized
environmental housing. All electrical connections
are via a single 39 pin rear panel connector. Table
1 lists electrical, mechanical, and environmental
specifications for the 2740 Camera.
Video output may be provided by an optional
fiber optic connector added on the rear panel.
When this option is selected, the 75 ohm output
on the 39 pin connector should not be terminated.
Any temporary connections to this 75 ohm output
for maintenance purposes should be done with a
short 75 ohm coax cable to avoid any “stub” effect
that may cause ghosting in the video.
The Camera operates with either NTSC or
PAL format, depending on the model. Both of
these formats are available in a high-sensitivity
version.
This Camera operates at an internal clock rate
of 28.6363 MHz (NTSC) or 28.375 MHz (PAL).
If the phase adjust line lock option is installed,
the vertical interval of the camera is referenced to
the 60 Hz power input for NTSC (or the 50 Hz
power input for PAL). A six position switch on
the rear panel then makes it possible to shift
this reference in 60 degree increments so that
the camera can be phased with other cam-
eras in the system that may not have the
same power line phase reference. This phase
difference can occur either because the other
cameras are on a different phase of the power
source or perhaps because they are con-
nected to a power source operating from a
different transformer.
The Camera is available with either 115 V
ac or 24 V ac input power — depending on the
model. An internal 20 watt heater cycles on an
off at low environmental temperatures to maintain
temperature inside the housing at operating
levels.
When an optional zoom lens is installed,
dedicated pins on the connector provide for
control of zoom, focus, and iris. Pins are also
assigned for location of the lens zoom position.
When an optional ID generator is mounted
inside the camera housing, it can be programmed
to provide messages in the video. It also provides
barrel pressure and temperature when these
displays are turned on.
Programming and control of the ID generator
is via RS-422 on the rear panel multipin connec-
tor. Cohu’s Win MPC graphical user interface
(GUI) software can be used to program these
messages. (WinMPC is available at no cost from
the cohu-cameras web site or by mail on CD.) —
or the system control software can be used if it
has been implemented with the proper protocol
messages.
If either shuttering or a manual gain setting is
desired, these setting must be performed before
the camera housing is sealed and pressurized.
Changing either of these optional settings requires
complete disassembly of the camera housing. It
must then be re-sealed, purged with dry nitrogen,
and pressurized with the dry nitrogen before
returning to service. For more information about
the internal camera module refer to Cohu Techni-
Figure 2. Sensor Wavelength
Response Characteristics
500
400 600 700 1000
900
800
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Wavelength (nm)
Relative Response
Standard Sensitivity
Enhanced Near IR
Sensitivity
Note: Both curves are normalized to 1.0 and thus the graph does not show comparative output levels

46X-1048B
2740 CAMERA INSTALLATION AND OPERATION
Table 1. Specifications
ELECTRICAL
Format
RS-170: 1/2-inch interline transfer monochrome CCD operating in field mode or
CCIR: 1/2-inch interline transfer monochrome CCD operating in field mode
( both available with extended near IR sensitivity)
Pixels 768 × 494 RS-170; 752 × 582 CCIR
Pixel Cell Size 8.4 (H) × 9.8 (V) µm RS-170 8 .6 (H) × 8.3 (V) µm CCIR
Resolution 580 HTVL (RS-170) 560 HTVL (CCIR)
Internal Clock 28.6363 MHz (RS-170) 28.375 MHz (CCIR)
Sync Internal crystal, or rear panel switch adjustable line lock, depending on model
Frame Rate 30 fps (RS-170); 25 fps (CCIR)
Sensitivity, Faceplate
Full video, max gain, agc off: Standard: 0.0012 lux E xtended: 0.0009 lux
80% video, max gain, agc off Standard: 0.0010 lux E xtended: 0.0007 lux
Agc On, extended sensitivity sensor: 0.28 lux, nominal min gain; 80% video, max gain, 0.0007 lux
Gamma 0.6 normal fixed (optional fixed 0.45 or 1.0)
Sharpness Circuit None used
Gain 0 to 46 dB gain control — either agc or internal manual adjustment
Shutter 1/60 (1/50 CCIR) to 1/100,000 sec; 8 steps (Internal switch access)
S/N 58 dB max; 10 dB S/N with 46 dB gain (0.6 gamma)
Spectral Response See figure 2
Power Input 24 V ac ±10 % or, depending on model,
115 V ac ±10 %
Power Consumption 30 W ; heater draws an additonal 20 W each time it cycles on in cold weather
Video Output RS-170 or CCIR, depending on model
Fiber optic ST connector output optional
Lens Control Auto iris (video style) and dc iris; zoom lens optional
MECHANICAL
Dimensions 21 inch long × 5.2 inch high (533 x 132 mm), without sun shield. See figure 4
Weight 10 lb (3.9 kg), less lens
Camera Mount 5 each 1/4-20 threaded holes on mounting base attached to barrel housing
Connectors 39-pin Bendix PT07C-20-39P, Schrader valve for pressure charging with dry nitrogen, pressure
relief valve, optional fiber optic connector
ENVIRONMENTAL
Temperature
-20 to 60 °C (-4 to 140 °F) operating
-40 to 60 °C (-40 to 140 °F) operating with heaters
-30 to 85 °C (-22 to 185 °F) non operating
Humidity Up to 100 % realtive humidity
Vibration (less lens) Sine vibration from 5 to 60 Hz, with 0.082 inch total excursion (15 g's at 60 Hz)
Random vibration from 60 to 1,000 Hz, 5 g's rms (0.027 g2/Hz without damage
Shock (less lens) Up to 15 g's, 11 ms, in any axis under non-operating conditions, MIL-E-5400T, paragraph 3.2.24.6
Altitude Sea level to equivalent of 3,000 meters (10,000 feet) 508 mm / 20 inches of mercury)
Air Contaminants Withstands exposure to sand, dust, fungus, and salt atmosphere, per MIL-E-5400T, paragraph
3.2.24.7, 3.2.24.8, and 3.2.24.9.
Explosion MIL-E-5400T, paragraph 3.2.24.10
Acoustical Noise Greater than 150 dB continuously for 30 minutes
Immunity EN61000-4-3, -4-6, -4-8 interference immunity tests

5
6X-1048B
2740 CAMERA
INSTALLATION AND OPERATION
SERIES
POWER
VIDEO FORMAT / SENSOR
4.5-inch
environmental
camera
4 24 V ac input
Power
5 115 V ac input
Power
ACCESSORIES
LENS
2 RS-170 1/2-inch standard sensitivity
3 RS-170 1/2-inch extended near ir sensitivity
5 CCIR 1/2-inch standard sensitivity
6 CCIR 1/2-inch extended near ir sensitivity
SYNC
1 Internal crystal
2 Line lock
0 None
4 ID generator
5 Fiber optic video
6 ID generator and
fiber optic video
IRIS
0 Auto/dc iris
3 Electronic iris
274 x — x x x x xxxx
Figure 3. Model Number Interpretation Diagram
cal Manual 6X-1040 (2700 camera) — available on
the cohu-cameras web site.
A model number interpretation diagram ap-
pears in figure 3. That diagram shows the various
basic configurations of the Camera. An optional
sun shield is also available but it is not modeled
into this number sequence.
The following options are available for the
camera:
1. Fiber optic video output
2. ID generator
3. Variable phase line lock
4. Either manual iris lens, auto iris lens, dc iris
lens, or zoom lens
5. Sunshield
1.1.1 Sensor Characteristics
Figure 2 shows the typical response charac-
teristic across relevant wavelengths of the sensor .
This chart shows both the standard sensitivity
curve and the enhanced sensitivity curve.
The camera lens and the window in the barrel
housing will have a slight impact on these curves.
These characteristic curves apply to both
NTSC and PAL sensors.
1.2 Mechanical Characteristics
Dimensions are shown in figure 4. The Cam-
era consists of a sealed and pressurized 21 inch
long barrel housing attached to a mounting base
with two stainless steel straps.
An optional sun shield can be mounted over
the housing to prevent heat build up from direct
sun light on the barrel. This sun shield extends
beyond the ends of the barrel about three inches
at each end. It can provide some protection from
direct sun exposure on the camera lens in certain
situations.
All electrical connections are made via a 39-
pin connector located on the rear panel. A fiber
optic option makes video available from a fiber
optic connector located on the rear panel. Video
from the 39 pin connector, then, should not be
used.
A Schrader valve (car tire type valve) on the
rear panel provides for pressurizing the housing
with dry nitrogen. This valve can be used to
occasionally add dry nitrogen as necessary to
maintain pressure in the barrel at about 5 psi (35
kPa).
A pressure relief valve on the rear panel
releases pressure at 20 psi (138 kPa) to prevent
extreme over-pressurization of the housing.

66X-1048B
2740 CAMERA INSTALLATION AND OPERATION
The mounting base for this camera has five
1/4-20 holes down the center line. This mounting
base plate aluminum is 1/4-inch thick.
At least two of these threaded holes must be
used to secure the camera to its mounting
platform. Use high quality grade 316 stainless
steel bolts and lock washers.
The threads on these bolts should extend
beyond the camera baseplate by at least 1/16
inch to ensure that at least one full thread is
exposed. But the bolts must not extend beyond
the camera base plate more than 3/8 inch or they
could bottom out on the barrel housing.
2.0 INSTALLATION
In addition to the actual installation requirements,
this section covers a number of other items
including proper shipping and handling of the
Camera.
2.1 Unpacking and Receiving
Inspection
This item was thoroughly tested and carefully
packed in the factory. Upon acceptance by the
carrier, they assume responsibility for its safe
arrival. Should you receive this item in a dam-
aged condition, apparent or concealed, a claim
for damage must be made to the carrier .
If a visual inspection shows damage upon
receipt of this shipment, it must be noted on the
freight bill or express receipt and the notation
signed by the carrier's agent. Failure to do this
can result in the carrier refusing to honor the
claim.
When the damage is not apparent until the
unit is unpacked, a claim for concealed damage
must be made. Make a mail or phone request to
the carrier for inspection immediately upon
discovery of the concealed damage. Keep all
cartons and packing materials.
Since shipping damage is the carrier's re-
sponsibility, the carrier will furnish you with an
inspection report and the necessary forms for
filing the concealed-damage claim.
To return the product to the factory for service,
please contact the Customer Service Department
for a Return Authorization (RA) Number.
2.2 Static Discharge Protection
Procedures in this manual do not require entry
into the housing of the Camera. But in the event
that a disassembled camera is being handled, the
following precautions should be followed:
CAUTION
This Camera contains sensitive devices that can be
damaged by static discharge. Use appropriate static
control methods when working inside the Camera.
Components used in modern electronic
equipment, especially solid state devices, are
susceptible to damage from static discharge. The
relative susceptibility to damage for semiconduc-
tors varies from low with TTL to high with CMOS.
Most other semiconductors fall between TTL and
CMOS in susceptibility to static discharge.
As a minimum, therefore, observe the follow-
ing practices when working inside this or any other
electronic equipment:
1. Use conductive sheet stock on the work bench
surface.
2. Connect the sheet stock to ground through a 1
megohm or greater value resistor.
Table 2. Items Supplied
ITEMS SUPPLIED
ITEM DESCRIPTION
1 Camera Barrel
2Base
3Stainless steel base-to-barrel
attachment straps (2)
Note: These items are supplied as
one assembly

7
6X-1048B
2740 CAMERA
INSTALLATION AND OPERATION
3. Use a wrist strap connected to ground through a
1 megohm or greater value resistor when
working at the bench.
4. Maintain relative humidity of the room above 30
percent. This may require a room humidifier.
Working on circuits with relative humidity below
30 percent requires extraordinary procedures not
listed here.
5. Use antistatic bags to store and transport an
exposed chassis, circuit boards, and compo-
nents. Use new antistatic bags. Old, used bags
lose their static protection properties.
This list serves as a reminder of the minimum
acceptable practices. Be sure that all static
discharge devices at the work bench are properly
installed and maintained. Standard grounding
mats and wrist straps purchased for use at work
benches are supplied with leads having current
limiting resistors for safety. Never substitute with a
grounding lead not having the resistor.
2.3 Equipment Supplied
The camera consists of a single environmen-
tal housing with attached mounting base. Cam-
eras intended for use outdoors typically are fitted
with an optional sun shield assembly that wraps
around the top half of the camera and extends
about three inches beyond the housing at each
end.
This sunshield minimizes heat buildup inside
the camera by shielding it from the direct rays of
the sun. It can also provide some protection from
lens flare in certain situations.
2.4 Equipment Required but Not
Supplied
As a minimum the camera requires a source
of operating power, a monitor on which to view the
scene, an interconnection cable, and a computer
running the Cohu WinMPC software for setup of
the ID generator if this option is installed.
This software is available at no cost as a
download from Cohu Electronics (www .cohu-
cameras.com) or by mail on a CD.
Communications with the optional ID genera-
tor must be via RS-422. Since the serial port on
most PC computers is likely to be RS-232, a 232/
422 converter will likely be required; however,
computers without either a 232 or 422 serial port
will likely have a USB port. In this case a USB-to-
422 converter will be required.
Installing the camera will also require grade
316 stainless steel mounting hardware and a
platform of some type on which to mount it.
2.5 Cabling Requirements
A single 39-pin connector on the rear panel
provides all electrical connections for the Cam-
era. See figure 5 for a typical system intercon-
nection cable.
If the optional fiber optic ST connector is
mounted at the rear panel to provide video output,
a mating ST connector with fiber optic cable
must be used to interconnected with it.
2.6 Power Requirements
The Camera is available as either a 24 V ac
or a 115 V ac version. Even though a Camera will
be configured for only one of these input voltages,
they are applied to different pins on the rear panel
connector.
A line-lock version of the Camera has a six
position phase switch on the rear panel. See
section 2.8.
Table 3. Rear Panel Connector and
Mating Cable Plug
REAR PANEL CONNECTOR MATING CABLE PLUG
Cohu 1310225-004
Bendix PT07C-20-39P
Cohu 1310230-005
Bendix PT06A-20-39S(SR)
Straight potting sleeve
Cohu 1310216-002
90° strain relief
1310441-001 and
straight potting sleeve
1310216-004
Note: Mating Cable Plug requires either the -002 straight potting sleeve or the 90 degree
strain relief with the -004 potting sleeve.

86X-1048B
2740 CAMERA INSTALLATION AND OPERATION
Figure 4. Dimensions, Model 2740 Camera
2.7 Mounting Requirements
The dimensions shown in figure 4 illustrate
characteristics of the camera related to securing it
to a pan-and-tilt unit, pedestal base, arm, or
similar mounting platform.
The five 1/4-20 holes on the bottom of the
camera mounting base are threaded through 1/4-
inch thick aluminum plate.
The bolts used to hold the camera to a
mounting platform should extend at least 1/16 inch
beyond the 1/4-inch camera base plate so that a
full thread is exposed. Bolts extending more than
3/8 inch beyond the camera base plate could jam
against the barrel housing of the camera. This
should not be allowed to happen.
2.8 Line Lock Operation
The line lock version of this Camera relies on
a sync reference derived from the ac power line in
place of an internal crystal oscillator as the refer-
ence source.
With equipment operating from different
phases of the power line, or perhaps off a different
transformer or other source, a typical step-phase
change in 60 degree increments makes it possible
to match with the vertical interval of other cameras
or equipment in the system.
2.9 Installation Procedure
Installing the Camera is straightforward. If it is
known that the internal camera module control
functions are properly set, it is only necessary to
mount the Camera to a suitable base, mate the
rear panel connector, and apply power. This
assumes the other end of the cable is properly
connected to a source of power, a tv monitor, and
any other required equipment.
See figure 5 for the wiring diagram of a typical
cable to use with the Camera. Not all of the
connections shown may be required. As a mini-
mum, this cable must provide power to the cam-
era and video to a tv monitor (unless the optional
fiber optic video output option has been installed).
Additional connections are required when either a
zoom lens or the ID generator option is installed.

9
6X-1048B
2740 CAMERA
INSTALLATION AND OPERATION
Figure 5 . Typical Interconnection Cable

10 6X-1048B
2740 CAMERA INSTALLATION AND OPERATION
2.9.1 ID Generator Messages (Option)
Entering messages into the optional ID gen-
erator requires use of either Cohu’s WinMPC
maintenance software or the system control
software if that software has been implemented
with the proper Cohu protocol messages (and
RS-422 system communications is available).
WinMPC can be obtained at no cost from the
cohu-cameras.com website or by mail on CD.
The ID generator messages are programmed
in via RS-422 on the 39-pin rear panel connector.
Since the serial port on a computer is typically an
RS-232 port, a 232 to 422 converter will probably
have to be used for this connection. It is recom-
mended that a B&B model 422PP9TB converter
be use (Available from Cohu as part number
3010100-001). There are subtle differences
among these types of converters and not all will
work in this application.
If the computer does not have an RS-232 port
it likely will have a USB port. In this case, a USB-
to-422 converter will be required.
WinMPC (or properly configured system
control software) can also be used to turn on and
off a display of internal housing pressure and
temperature when the ID generator option is
installed.
Messages to be displayed by the ID generator,
an indication of the nitrogen pressure, and interior
barrel temperature readings can also be controlled
by the system software if the correct protocol
messages have been implemented and RS-422
communications is established with the camera.
2.9.2 Rear Panel Features
All interconnections with the camera are via a
39-pin Bendix type connector (figures 6 and 7) —
unless the fiber optic video option is installed in
which case video leaves the camera on an ST
type fiber optic connector (figure 8).
2.9.2.1 39-pin Connector
Table 4 lists all pin functions of this connector .
Note that certain pins are not used and others
may not be used depending on what options are
installed in the camera.
Figure 6 . Rear Panel Features
(basic camera)
ABC
D
E
F
G
H
J
KL
M
N
P
R
S
T
UVW XYZ
a
b
c
d
e
f
g
h
ij
k
l
r
m
n
p
Looking at rear panel of camera.
Same pin orientation as the rear
wiring view of mating connector
Figure 7. Connector Pin Orientation
Position return pins are used only when the
camera has been mated with a zoom lens.
The TXD, TXD (not) and RXD, RXD (not) RS-
422 pins are used only when the related ID gen-
erator circuit board option is installed.
Note that separate pins are dedicated to 115 V
ac and to 24 V ac input power. The camera will be
internally configured to accept only one of these
input voltages.

11
6X-1048B
2740 CAMERA
INSTALLATION AND OPERATION
Table 4. Pin Functions,
Rear Panel Connector
PIN FUNCTION
A 24 V ac
B position reference return
Cnot used
D focus position
ERXD
Fnot used
Gnot used
Hnot used
J ground, video out
K video out
L ground
Mnot used
N ground
P shield (zoom lens controls)
R zoom
Sfocus
Tiris
U lens common (ground)
V 115 V ac low (neutral)
W 115 V ac high (line)
X ground, ac power (115)
Y zoom position
Z ground
aRXD (not)
b position reference
c auto/manual iris select
d 24 V ac input
enot used
f ground
gnot used
hTXD (not)
iTXD
jnot used
k ground (RS-422)
lnot used
mnot used
nnot used
pnot used
rnot used
Figure 8. Rear Panel Features
(optioned camera)
2.9.2.2 Connector Tx (Transmit) and
Rx (Receive) Conventions
Table 4 and figure 5 show pin functions for
RS-422 connections. The Tx+ Tx- and Rx+ Rx-
notations for these RS-422 connectors and all
other RS-422 connectors in a system using this
notation cause much confusion for field installers.
There is a tendency to want to connect Tx to Tx
and Rx to Rx. This almost always is wrong.
The Tx+ output of one piece of hardware
should go to the Rx+ input of another. And Tx-
goes to Rx-. Note that “not” can be used for the “-”
(minus) designation, e.g., Tx (not) and Rx (not).
To add to the confusion Tx and Rx are not
universally used notations for the same functions.
Some times “Command Out” is used for Tx and
“Command In” for Rx. Other naming conventions
are also used among different equipment and
cables.
Because RS-422 provides bidirectional com-
munications over the same cable (although on
different wire pairs) a connector can be an input at
one moment and then an output milliseconds later
(RS-422 half-duplex). Thus, markings that would
attempt to label connectors as either input or
output would be somewhat arbitrary .
With RS-422, the wire pairs themselves,
though, pass data in only one direction. For

12 6X-1048B
2740 CAMERA INSTALLATION AND OPERATION
example, output pins on connector A must be
routed to the input pins of connector B. And to get
data back the other direction, the output pins on B
must then be connected to the input pins on A.
The concept is simple but in practice the labeling
found in the field can sometimes be confusing.
If any confusion exists it is best to contact the
Customer Support department at Cohu or your
local Cohu representative.
2.9.2.2 Fiber Optic Connector (option)
An ST type connector is mounted on the rear
panel when the fiber optic video output option is
installed in the camera. This connector supports
an 850 nm multimode connection with 62.5 µm
fiber. Optical budget is 13 dB. This module is a GE
Interlogix Fiber Options model S700VT-TST.
The companion units are their model S700VR
and S702VR receivers. Receiver modules from
other manufacturers should be tested before
committing to their use with this camera. Consult
with a Cohu Electronics Applications Engineer or a
Cohu Field Representative for further information.
Using 75 Ohm Video Output when Fiber Optic
Option Installed
When the fiber optic video output option is
installed in the camera, video from pins K and L on
the 39 pin connector cannot be used for system
video connections because this is not an isolated
output. The input to the fiber optic module inside
the camera is internally terminated with 75 ohms
and pins K and L merely tap off at this module
input. Using the K and L output pins would require
double termination.
But for temporary maintenance functions, pins
K and L (video) could be used in addition to this
fiber optic output, if desired, so long as only a
short cable is connected to these pins and no
termination is used. Monitors used for servicing
video equipment usually have a switch to insert or
remove the 75 ohm termination on their input.
A long cable could act as a “stub” to cause
interference such as ghosting in the video signal.
Terminating pins K and J when the fiber optic
option is installed would cause the video level to
drop to one-half of normal.
2.9.2.3 Phase Adjust Line Lock Switch
(Option)
If the vertical interval of a camera must occur
at the same time as the vertical interval of other
equipment in the system, a six position switch on
the rear panel provides for six 60-degree incre-
ments of shift when the line lock option is installed.
Equipment operating on other phases of the
power line or perhaps from a different transformer
will typically have phase differences in 60 degree
increments.
2.9.2.4 Schrader Valve
The Schrader valve installed on this camera is
functionally identical to those used for car tires —
but this valve should be used to introduce only dry
nitrogen into a camera housing.
During assembly cameras are purged of
normal room air (which typically has a high relative
humidity) by flowing dry nitrogen into the Schrader
valve and out the pressure relief valve. This relief
valve is held open to aid in the flow of nitrogen out
of the camera. The PRESS. RELIEF bolt (figure 6)
can also be removed when it is desired to flow dry
nitrogen through the housing.
This purging process removes moist room air
from inside the camera to provides an internal
relative humidity of about five percent.
A camera is typically pressurized to 5 psi (34
kPa). Pressure can be allowed to go below this —
even down to one or two pounds so long as the
pressure does not ever become zero.
Figure 9. Humidity Indicators
(Blue is Normal)

13
6X-1048B
2740 CAMERA
INSTALLATION AND OPERATION
An occasional recharge of dry nitrogen can be
used to maintain pressure near 5 psi (34 kPa). If
pressure continually drops it is an indication of a
slow leak and the camera requires maintenance.
These pressure references are gauge pres-
sures (psig). They are relative to the altitude
above sea level at which they are being mea-
sured.
2.9.2.5 Pressure Relief Valve
The pressure relief valve opens at about 20
psi (138 kPa). This valve should be manually lifted
off its seat when it is desired to flow dry nitrogen
through the camera to purge any moisture laden
atmospheric air from the camera.
This valve has short section of clear tubing
around it to prevent the pop-up stem from acci-
dentally being moved and thus releasing pres-
sure. This plastic will have to be taken off to gain
access to the pop up valve for manual release of
pressure. Be sure to install the tubing again after
purging and pressurization is completed.
2.10 Front Window Features
The camera lens is mounted behind the
window at the front of the camera housing. Near
the bottom of this window are three circular disks
inside the camera housing. The disk on the left is
labeled 10, the middle one 20, and the one on the
right 30. See figure 9.
When relative humidity inside the camera is
below 10 percent, all these disks will be blue in
color. If humidity inside the camera should for
some reason rise above 10 percent, the 10 disk
will change color to pink. Likewise, if relative
humidity rises above 20 or 30 percent the related
disk will also turn pink. These disks can be used
as an indication of the approximate relative humid-
ity inside the camera. It should be below 10
percent and all disks blue in color.
If these disks turn pink it is an indication that
pressurization with dry nitrogen has dissipated
and moisture laden air has entered. Or it could
mean that the camera was not properly reas-
sembled and purged with dry nitrogen during
maintenance procedures.
It may be possible to flow dry nitrogen through
the camera for several minutes in an attempt to
purge moist air from the camera and thus turn a
humidity indicators blue again — but this could
expend a large amount of dry nitrogen. And if a
desiccant pack inside the housing has absorbed
moisture (which is likely) the camera would then
require disassembly to replace this pack.
Once an internal desiccant pack absorbs
excess moisture it has to be removed and either
oven dried for at least 16 hours or replaced by a
fresh, dry pack that has been kept in a tightly
sealed container.
When a camera is being assembled warm air
is blown across these humidity indicators with a
heat gun to remove moisture and turn them blue.
Stripping them of moisture by flowing dry nitrogen
across them can require far more dry nitrogen
than is required to purge moisture laden air from
the housing components.
2.11 Preparation for Shipment and
Storage
For storage periods exceeding about one
month, seal the unit in a vapor-proof bag contain-
ing a fresh desiccant pack.
Maintain the Camera storage environment
within a range of -30 to 85 °C (-22 to 185 °F).
For shipment, package with enough foam
padding or other packing material to prevent
shipping damage that can occur. The original
shipping carton is a good container if it has not
been damaged or subjected to excessive mois-
ture. For shipping to the factory by Common
Carrier, use the following address:
Cohu Electronics
12367 Crosthwaite Circle
Poway, CA 92064-6817
Please contact the Customer Service Depart-
ment of Cohu Electronics for a Return Authoriza-
tion (RA) number before sending any shipments
to the factory:

14 6X-1048B
2740 CAMERA INSTALLATION AND OPERATION
[email protected]
or
858-277-6700 extension 5738
Prominently display the RA number on the
outside of the shipping container(s) and on paper-
work contained inside. Give a brief description of
why the equipment is being returned and list the
symptoms of any problems being experienced
with the equipment.
3.0 OPERATION
After the Camera is installed, operation of the
Camera requires minimum attention. If a zoom
lens is being used, the zoom in/out and focus
may have to be changed occasionally .
Optional ID generator messages and readout
of internal housing pressure and temperature may
be visible — or they can be turned on and off if the
proper protocol messages have been imple-
mented and RS-422 communications exists with
the camera.

6X-1048B 15
INSTALLATION AND OPERATION
2740 CAMERA
Revision History
Revision Date Comments
Rev B 05/10/2011 • This manual has been revised to comply with the latest engineering requirements. See ECO
030972 for the list of changes.
WARRANTY
Please refer to the COHU website for product warranty information:
www.cohu-cameras.com