A
DJM3
IOM-17
12 of 27 Mar 99 R3
BMS
RESET
(continuous
blower
operation
only)
DIP switch one must be on to activate BMS reset. This option requires an analog voltage or current
signal to be wired to the optically is and ‐ terminals. The analog input signal proportionally
increases the calculated discharge air set‐point. The calculated discharge set‐point equals the dial
discharge set‐point plus the input signal multiplied by a reset ratio factor.
The maximum amount of reset is adjustable from 15°F (8°C) to 60°F (33°C). The maximum discharge
temperature (dial set‐point plus reset) is limited to 120°F (49°C). The BMS reset option is activated by
DIP switch 1.
Note: As standard, the DJM3 is designed to operate with 4‐20 mA or 2‐10 Vdc into a 500‐ohm input
impedance. Some BMS devices may not have enough power (Volt‐Amps) to provide a full 10
VDC when connected to a 500‐ohm load. The input resistance for this operation can be
increased to 1500 ohms by cutting resistor R43. To cut this resistor you must turn the board
over. It is located on the back of the larger board, just below the DIP switch block and beside
Pot Reset Ratio. This is a 1‐watt, 680‐ohm resistor colours blue, grey, brown, gold.
BMS reset is not truly linear. Reset will usually begin at about 4 volts. Following, is an example of reset
from one application that gives a 13°C or 24°F reset.
CALCULATED SETPOINT FROM BMS RESET APPLIED TO + AND –
TABLE 10
Current
Reset
Voltage
Reset
Calculated Setpoint
mA
Vdc
°C
°F
‐
0
13
55
3
3
13.5
56
5
4
14.5
58
12
6
16
61
‐
7
18
65
16
8
20
68
‐
9
23
75
20
10
26
79
AMBIENT
RESET
(continuous
blower
operation
only)
This option requires DIP switch 2 to be on and an ambient sensor (Johnson Controls TE 6000‐960)
wired to terminals X and Z. The discharge air set‐point will be reset upwards based on the ambient
temperature. Ambient temperatures below 70°F (21°C) will gradually increase the calculated discharge
air set‐point. The maximum increase in the discharge temperature will be reached when the ambient
falls to 20°F (‐7°C). The amount of reset is dependent on the position of Reset Ratio Pot and the
discharge set‐point as set on the dial.
(The discharge set‐point will be reset below master set‐point if ambient is above 70°F (21°C). In most
cases when the outside ambient is above 70°F (21°C), the heat will be off.)
