Watlow Series 94 - Manual (Page 10)

Sensor Installation Guidelines
We suggest you mount the sensor at a location in your process or system where
it reads an average temperature. Put the sensor as near as possible to the mate-
rial or space you want to protect. Air flow past this sensor should be moderate.
The sensor should be thermally insulated from the sensor mounting.
See Chapter 4 for more information on DIP switch location and orientation.
Input Wiring
Figure 2.4a – Thermocouple
Extension wire for thermocouples must be of the same alloy as the thermo-
couple itself to limit errors.
DIP Switch orientation
Figure 2.4b – RTD (2- or 3-Wire) 100
Ω
Platinum
There could be a + 2°F input error for every 1
Ω
of lead length resistance
when using a 2-wire RTD. That resistance, when added to the RTD element
resistance, will result in erroneous input to the instrument. To overcome
this problem, use a 3-wire RTD sensor, which compensates for lead length
resistance. When extension wire is used for a 3-wire RTD, all wires must
have the same electrical resistance (i.e. same gauge, same length, multi-
stranded or solid, same metal).
DIP Switch orientation
O
N
↑
1 2
S1
S2
S3
2
3
5
3-wire RTD
S1
S2
S3
2
3
5
2-wire RTD
Jumper
Terminals
3 and 5.
O
N
↑
1 2
T/C
+ 3
- 5
Install and Wire
2 . 4 ■ I n s t a l l a n d W i r e W a t l o w S e r i e s 9 4
Ó
WARNING: To avoid elec-
tric shock and damage to
property and equipment,
use National Electric
Code (NEC) safety prac-
tices when wiring and
connecting this unit to a
power source and to elec-
trical sensors or peripher-
al devices. Failure to do
so could result in injury or
death.
NOTE:
When an external device
with a non-isolated circuit
common is connected to
the dc output, you must
use an isolated or un-
grounded thermocouple.