Page 32 IM 781-2
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CAUTION
Ground loop current hazard.
Can cause equipment damage.
If analog inputs/outputs on a MicroTech II Remote I/O Module are connected to more than one external device,
the connected analog outputs/inputs of those devices must be isolated from ground. If they are not, ground loop
currents could occur which could damage the remote I/O module and connected equipment. If external devices
do not have their analog outputs/inputs isolated from ground, condition the signal with a signal isolator on each
device.
1. Cooling Tower VFD Speed Feedback 1-16 (Optional)
The cooling tower VFD speed feedback AI’s can be wired to a VFD AO to show each VFD’s actual speed in the form of
percent max speed. This value is for display purposes only; the CSM’s operation will not be affected by the actual speed of
any individual VFD. A cooling tower VFD AO can be wired to any AI on any remote I/O module (E, F, G, or H), they do
not have to be sequential. Typically the VFD speed feedback would be wired to the same AI number as the DO number
which enables that particular VFD.
Digital Inputs
Each remote I/O module is equipped with 4 digital inputs, which are set to receive digital inputs from external dry contacts.
1.
Cooling Load Pump Status (Remote I/O Modules A, B, and C – DI 1 and DI 2)
If the CSM is controlling cooling load pumps, flow must be proven after a pump has been enabled or a pump failure alarm
will be generated and the pump will be disabled. The flow proving device must close a normally open dry contact which is
wired to the associated digital input on the remote I/O module. The flow proving device (i.e. current switch, flow switch,
etc) is field supplied.
An open contact at a cooling load pump status digital input, along with an enabled cooling load pump digital output with
the same number, will activate an alarm after these conditions have been satisfied a period of time greater than the Pump
Status Check Delay Time (default = 30 seconds).
2. Cooling Tower Alarms 1-16 (Optional, Located on Remote I/O Modules E, F, G, and H – DI 1, 2, 3, and 4)
The cooling tower alarm is an option that will notify the CSM that an alarm has occurred on a cooling tower device. This
alarm is for display/notification purposes only; the CSM’s operation will not be effected by the occurrence of a cooling
tower alarm.
A normally closed dry contact is required for each output device (e.g., fan VFD, current switch, airflow switch, etc.) that
could fail when a cooling tower alarm input is to be used. Note that the dry contacts are field supplied. The dry contacts are
field wired to the cooling tower remote I/O modules (Modules E, F, G, and/or H depending on alarm requirements) digital
inputs (see Figure 27). A closed contact at a cooling tower alarm digital input, along with an enabled cooling tower digital
output with the same number; will activate an alarm after these conditions have been satisfied for 30 seconds.
Outputs
Analog Outputs
Each remote I/O module is equipped with two analog outputs. These analog outputs provide 0 to 10 VDC, 1-mA signals.
The remote I/O module’s analog outputs are isolated from ground as long as the 24-volt power supply does not have its
common (terminal 2) tied to ground. Do not wire the secondary side of this 24-volt transformer to ground. The analog
output common terminals are tied to each other (and the analog input common terminals). Ground loops could occur
through the remote I/O module if it is connected to two or more external devices that are not isolated from ground.
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