Thermo Scientific 3911, Operating Manual

Page: 22 / 76

| Product Description
5-2
|
Model 3900 Series Forma
Chapter 5
4-20 Milliamp Output
The environmental chamber is equipped with 4-20mA output for the remote transmission
of temperature, humidity and CO
2
data. A terminal strip is located on the back of the
environmental chamber for convenience. Refer to Figure 5-2 for terminal pin
identification.
Figure 5-2
Terminal Pin Identification
Remote Alarm Contacts
Remote alarm connections are also included on the terminal strip providing Normally
Open (N.O.) and Normally Closed (N.C.) contacts. C is the Common terminal. The remote
alarm will activate when either the chamber’s temperature, humidity, or CO
2
go out of the
set alarm limits.
IR CO
2
Option
This section applies to units with the IR CO
2
option only.
Connect the CO
2
Source
For the most economical use, the liquid CO
2
supply tanks should be without siphon tubes,
so that only CO
2
gas enters the environmental chamber injection system. Two tanks may
be joined together with a manifold to ensure a continuous CO
2
supply.
Install a two-stage pressure regulator, with indicating gauges, at the supply cylinder
outlet. The high-pressure gauge should have an indicating range of 0 to 2000 psig to
monitor tank pressure. The low-pressure gauge should have an indicating range of 0 to
30 psig to monitor input pressure to the chamber injection system. A suitable two-stage
pressure regulator is available.
Temperature
4-20mA
(-20 to 80°C) Humidity
4-20mA
(0 to 100%)
Remote Alarm
30V 1A max.
CO
2
4-20mA
(0 to 20%)
NOTE
When the chamber temperature control setpoint is changed, the undertemp
safety thermostat must be reset to accommodate the change.
NOTE
The undertemp control is not directly calibrated. The numbers on the dial are
for reference only.