AERCO BMS II BOILER - Manual (Page 17)

INSTALLATION
2-5
2.5 SENSOR INSTALLATION AND WIRING
There are two types of sensors that can be installed: a Header Sensor and an Outside Air Sensor. If
desired, an optional Return Sensor can also be installed. The Return Sensor is the same type and part
number as the Header Sensor, however it is only used for `external monitoring purposes. The Header
Sensor is required for all modes of operation. The Outdoor Air Sensor is required for operation in the
Outdoor Reset Mode.
All Sensor wiring should be run separately from power wiring to avoid inducing electrical noise on the
sensor wiring.
Header Sensor
A Header Sensor Kit, (part no. 122790) is provided with the BMS II. This Kit contains the Header Sensor
(64038), a Thermowell (122758) and some heat conductive grease which MUST be used with the Sensor.
When installing the Sensor, use a 1/2 inch NPT tapped coupling or a 4 x 4 x 1/2 inch Tee fitting. Shielded
pair, 18 AWG cable (Belden # 8760 or equiv.) is recommended for Header Sensor wiring. The Header
Sensor must be installed between 2 and 10 feet downstream of the LAST boiler in the boiler plant’s
supply water header. Install the Header Sensor as follows:
NOTE
The Header Sensor is a thermistor type sensor. The Resistance vs.
Temperature Chart for this sensor is provided in Appendix D. The length
of the Header Sensor wire leads should not exceed 600 feet.
1. Refer to Figure 2-3 for the Header ‘Sensor installation details.
2. Install the Header Sensor and Thermowell into the 1/2 inch NPT tapped coupling or a 4 x 4 x 1/2 inch
Tee fitting using heat-conductive grease provided. This will aid in its response.
3. For proper response, ensure that the Header Sensor probe is inserted at least 2 inches into the water
flow.
4. Using shielded pair cable (Belden #8760 or equiv.) connect the Header Sensor leads to HDR SEN
terminals 4 and 5 on the BMS II. There is no polarity to observe when making these connections.
5. Terminate the cable shield at SHLD terminal 3 of the BMS II. DO NOT terminate the shield at the
Sensor end of the cable.
Return Sensor
As mentioned in paragraph 2.5, the Return Sensor is identical to the Header Sensor. Therefore, if a
Return Sensor is being installed, another Header Sensor Kit (part no. 122790) is required. The Return
Sensor should be installed in the boiler water return line within 3 feet of the first boiler in the boiler plant’s
return water line. The installation details shown in Figure 2-3 for the Header Sensor also apply to the
Return Sensor. If used, install the Return Sensor as follows:
1. Refer to Figure 2-3 and install the Return Sensor and Thermowell into the 1/2 inch tapped coupling or
or Tee fitting using heat conductive grease.
2. Using shielded pair cable (Belden #8760 or equiv.) connect the Return Sensor leads to terminals 6
and 5 on the BMS II. There is no polarity to observe when making these connections.
3. Terminate the cable shield at SHLD terminal 3 of the BMS II. DO NOT terminate the shield at the
Sensor end of the cable.