Lake Shore Model 218 Temperature Monitor User’s Manual
3-8
Installation
3.3.3.1
RELAYS (MODEL 218S only)
The Model 218 has eight relays most commonly associated with the alarm feature. If a relay is
inactive (Off), it is in its normal state of open or closed. When the relay is active (On), it is in the
opposite state. The relay contacts are isolated from the instrument ground. Connect to the relay
contacts through the terminal block (refer to Paragraph 3.3.3).
3.3.3.2
Analog Outputs (MODEL 218S only)
Analog Output 1 and 2 on the Model 218S rear panel are voltage outputs that can be used for
monitor applications (Figure 3-4). Their most basic function is a temperature monitor where they put
out a voltage proportional to temperature.
Both analog outputs are variable DC voltage sources that can vary from –10 V to +10 V. The
resolution of the analog output is 1.25 mV or 0.0125% of full scale. They can drive a resistive load
of no less than 1 k
Ω
. The output is short protected so the instrument is not harmed if resistance is
too small. It is not recommended because the additional load on instrument power supplies causes
noise on internal circuits.
It is not recommended to attach the analog output ground to a ground outside the instrument. The
output should be read by an instrument with an isolated or differential input wherever possible.
Connecting to an external ground can cause noise in the analog output voltage or the sensor input
measurement. If this cannot be avoided, try to keep the chassis of the two instruments at the same
potential with a ground strap. Connect to the analog out contacts through the terminal block (refer
to Paragraph 3.3.3).
3.3.4 Computer
Interfaces
Refer to Chapter 6 for details about the IEEE-488 (Model 218S ONLY) and serial computer
interfaces. Refer to also Chapter 5 for details on connecting the serial port to a printer.
