Digital Outputs - McQuay MicroTech II Installation Manual

Ground loop current hazard.
Can cause equipment damage.
If analog outputs/inputs on a MicroTech II Remote I/O Module are connected to more than one external device,
the connected analog inputs/outputs 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 inputs/outputs isolated from ground, condition the signal with a signal isolator on each
device.
1. Cooling Load Pump VFD Speed (Remote I/O Module A, B, C – AO 1 and AO 2)
If the CSM's Chilled Water Loop Modulation Control Option = Pump VFD, the CSM controls a cooling load pump with
variable frequency drive (VFD) to maintain a desired pressure differential across the chilled water loop. These analog
outputs are available to be wired to analog inputs on the VFD's controlling the pumps. All six analog outputs are controlled
to the same value.
2. Chilled Water Loop Bypass Valve (Remote I/O Module D – AO 1)
If the CSM's Chilled Water Loop Modulation Control Option = Chilled Water Loop Bypass Valve, the CSM modulates a
valve to maintain the differential pressure between supply and return water lines at the adjustable setpoint.
3. Cooling Tower Fan VFD (Remote I/O Module E – AO 2. Modules F, G and H – AO 1 and AO 2)
The CSM controls cooling tower VFD speed to maintain either the entering or leaving condenser water temperature at the
Cooling Tower Stage 1 Setpoint. All seven analog outputs are controlled to the same value.
4. Cooling Tower Bypass Valve (Remote I/O Module E – AO 1)
The CSM controls a tower bypass valve to maintain either the entering or leaving condenser water temperature at the Valve
Setpoint or the Stage Setpoint.

Digital Outputs

Each remote I/O module is equipped with four 230 VAC, digital outputs (i.e. relays). Two are normally open (N.O.) and
two are changeover (C.O.) relays. The normally open contacts on all four relays are rated for 6 amps continuous current
while the normally closed contacts on the C.O. relays are rated for 1 amp continuous current. These high-voltage relay
terminals are the orange touch-less terminals on the top of the module (separated from the low-voltage terminals).
If these relays are used for control of high-voltage devices, the wiring must be run separate from any low-voltage wiring. If
you are wiring to remote I/O modules mounted in the remote I/O panel and high-voltage devices are being switched, run
the wiring from these devices into the top or bottom of the remote I/O panel. Connect these wires directly into the touch-
less orange relay terminals on the high voltage side of the module. Wire the low-voltage and communication wiring into
the sides of the remote I/O panel and connect these wires directly into the brown terminals on the low-voltage side of the
module.
Do not mix low-voltage and high-voltage signals on the relay side of the remote I/O modules.
Equipment malfunction can result.
1. Cooling Load Pump #1-#2 (Remote I/O Module A – Relay 1 and Relay 2)
If the CSM will be controlling the cooling load pumps - Cooling Load Pump 1 Enable and Cooling Load Pump 2 Enable
relay outputs are used to start and stop pumps 1 and 2. When the proper signal is sent by the CSM through the pump digital
output, the pump will start.
2. Cooling Load Pump #3-#4 (Remote I/O Module B – Relay 1 and Relay 2)
If the CSM will be controlling more than two cooling load pumps - Cooling Load Pump 3 Enable and Cooling Load Pump
4 Enable relay outputs are used to start and stop pumps 3 and 4. When the proper signal is sent by the CSM through the
pump digital output, the pump will start.
IM 781-2
CAUTION
!
CAUTION
!
Page 33