Section 2
Page 2 - 10
MODEL 346 INSTALLATION AND OPERATION MANUAL
HA243821
Issue 5 Mar 98
2.4 CIRCUIT BOARD LINKS (Cont.)
2.4.1 INPUT CHANNEL CONFIGURATION RULES
1. If only one channel on a 3-channel card is to measure a direct thermocouple input, it must be Channel 1.
2. If more than one channel is to be connected for direct thermocouple, channel 1 MUST be one of those
channels.
3. If the channel 1 Link is set for ‘RTD’, no channel on the same board can be used for direct thermocouple input.
Note...
The thermocouple cold junction compensation (CJC) for all three channels on an input amplifier card is meas-
ured by the channel 1 circuitry.
2.4.2 CHANNEL THERMOCOUPLE / RTD LINK
The TC/RTD Link within each input amplifier's circuitry must be set to ‘TC’ (Thermocouples, Millivolt and Voltage
or Current inputs) or ‘RTD’ (Resistance Temperature Detector).
If the centre and ‘TC’ pins are connected, the channel is set up for thermocouples and other dc inputs. If the
centre and ‘RTD’ pins are connected, the channel is set up for RTDs.
2.4.3 THERMOCOUPLE FAILSAFE (UP - DOWN) LINKS
The UP/DOWN Link for each channel amplifier determines the open input (TC Break or Failsafe) direction for that
channel. This function does not operate if the other link for the channel is in the ‘RTD’ position. Should the input
go open circuit, the recorded and displayed values are driven beyond the established range limits in the chosen
direction, triggering any appropriate alarms as they go.
If the fail safe feature is not required, the link can be conveniently ‘parked’ on pin 2 at right angles to the rest of the
row of pins.
Note...
The fitting of up- or down-scale links causes a slight reduction in measurement accuracy. Thus to gain the
maximum from the measurement system, the fail-safe links should not be fitted.
2.4.4 CJC LINK
There is a link just behind the CJC sensor ‘finger’ on the rear edge of each input amplifier board.
If channel 1 (4) is set up to be connected to an RTD, the CJC link must be in the ‘RTD’ position. Channel 1 (4)
may then be connected only to a resistance thermometer. Channels 2 (5) or 3 (6) can be used either with
resistance thermometers or dc inputs, but NOT thermocouples.
If channel 1 (4) is set up to be connected to a thermocouple, then channel 1 (4) may be used to measure a
thermocouple or dc input but NOT an RTD input. Channels 2 (5) and 3 (6) can be used for thermocouples, dc
inputs or resistance thermometers.
