Minco Tel: 763.571.3121 • Fax: 763.571.0927 • www.minco.com 10
2. In uts
The CT224 can accept any com ination of the input types specified in Section 6 at the end of
this document. These may include RTDs, thermocouples, and 4-20mA transmitter loops.
However, some care must e taken when using multiple inputs so that a safe environment is
created for personnel and equipment. For instance, a CT224 should monitor sensors from
only one piece of equipment, especially if high voltage is present. Using this approach,
damage to other devices is greatly reduced, if a circuit fault should occur.
The CT224 does not have channel to channel isolation. This means that grounded
thermocouples cannot e used directly with the CT224. Ungrounded thermocouples may e
used. If grounded thermocouples are used, a device such a Thermocouple Isolator can e
utilized as a means to reak ground loops and provide proper inputs to the CT224.
Another consideration due to not having channel to channel isolation is that when using 4-
20mA inputs, all loops will share the same return path. Keep this in mind when planning the
system to ensure that it is safe to wire all loops together. It is the system designer’s
responsi ility to ensure that good safety measures are used. If unsure a out the safety
aspects of a system, call Minco for assistance.
Each input channel has 3 input terminals and a common earth ground terminal. The
terminals are la eled as A, B, C and D. Terminal D is connected to earth ground, when earth
ground is connected to the terminal lock as descri ed in Section 1, Controller Power. Input
wiring for the different input types is shown in Figures 7, 8, 9, and 10.
RTDs - RTDs Use three terminals per channel. Care should e taken to not exceed 30 ohms of
lead wire resistance. Chart 1 shows maximum lead wire length per lead of an RTD so as not to
exceed the 30 ohms maximum lead wire resistance. Leadwire for RTDs should e twisted and
shielded, this will reduce fluctuations in the readings due to noise.
3-wire RTD: The odd colored wire must e connected to terminal A of the input channel.
The other two wires can e placed in either order in B and C. If the RTD has a shield, place it
into terminal D. When adding leadwire to the RTD, e sure to use the same length and gauge
for each lead. The CT224 is a le to provide very good compensation for leadwire resistance
as long as each lead has the same resistance. Recommended Extension Leadwire: Belden
1031A or any other wire that is twisted and shielded is a good choice.
Leadwire
(AWG)
Ohms/Foot at
25ºC
30 ohms of
Resistance
18 .0065 4615
20 .0103 2912
22 .0165 1818
24 .0262 1145
26 .0418 717
28 .0666 450
Chart 1 – Leadwire Resistance per lead
