Despatch P1400+ Temperature Controller - Manual (Page 18)

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Contacts:- Arcing may occur across contacts when they open and close. This results in electrical
noise as well as damage to the contacts. Connecting a properly sized RC network can eliminate this
arc.
For circuits up to 3 amps, a combination of a 47 ohm resistor and 0.1 microfarad capacitor (1000
volts) is recommended. For circuits from 3 to 5 amps, connect two of these in parallel.
Figure 8. Contact noise suppression
4.6 Sensor Placement (Thermocouple or RTD)
If the temperature probe is to be subjected to corrosive or abrasive conditions, it must be protected
by an appropriate thermowell. The probe must be positioned to reflect true process temperature:
1. In a liquid media - the most agitated area
2. In air - the best circulated area
CAUTION:
The placement of probes into pipe work some distance from the heating vessel leads to
transport delay, which results in poor control.
For a two wire RTD a wire link should be used in place of the third wire. Two wire RTDs must only
be used with lead lengths less than 3 metres. Use of three wire RTDs is strongly recommended.