Lochinvar 1.0- 1.3- 1.5 operation manual Rate and Temperature Conversions, Deg C Deg F Voltages

Modbus Instructions

5Unit Operation (continued)

Rate and Temperature Conversions:

Rate

When issuing a rate command the rate can be communicated as percent modulation or a desired setpoint, depending on the setting of the BMS Type in the BMS Setup Menu.

The proper data format for the modulation percentage is the direct conversion to hexadecimal. This conversion can be accomplished through online number based converters or some scientific calculators.

For Example:

Rate %	HEX
0	00
20	14
45	2D
60	3C
80	50
95	5F
100	64

To send a desired setpoint, the hexadecimal value must be determined through linear interpolation of programmable parameters on the BMS Setup Menu:

-BMS temperature set-point at low analog input

-BMS temperature set-point at high analog input

These variables set the temperature values corresponding to the minimum and maximum voltage settings of the 0-10 volt signal. The defaults are as follows:

	DEFAULT		DEFAULT
PARAMETER	VALUES
	Deg C	Deg F	Voltages
BMS temperature setpoint at	21	69.8	2
low analog input
BMS temperature setpoint at	82	179.6	10
high analog input

For Example:

Send a setpoint of 110°F.

The formula to use for the interpolation is:

Rate Command =

(Desired Setpoint – BMS Temp at Low Analog Input) (High

Voltage-Low Voltage) + Low Voltage

(BMS Temp at High Analog Input – BMS Temp at Low

Analog Input)

From the default values:

Desired Setpoint = 110

BMS Temp at Low Analog Input =68

BMS Temp at High Analog=158

High Voltage =10

Low Voltage = 2

[(110-69.8)(10-2)/(179.6-69.8)] + 2 = 4.92 Volts

(4.92/10) x 100 = 49.2

49 = 31 Hexadecimal

A value of [00][31] in hexadecimal would be written to Holding register 40003 to issue a command for a 110°F setpoint.

Temperature

The SYNC boiler passes temperature data in degrees Celsius. Also, to accommodate decimal places the decimal value must be divided by 10.

Here are the conversions to and from Celsius:

T	= (5/9) * (T	-32)	T = (9/5) * T		+32
c	f		f	c

Example:

Outdoor temperature from remote sensor on BAS System = 80°F

80°F = 26.7°C

Data that needs to be transmitted is 26.7 * 10 = 267

Decimal	Binary	HEX
267	100001011	10B

Outlet temperature from unit sensor = 155°F

155°F = 68.3°C

Data transmitted from unit in HEX = 2AB = 683 683 ÷ 10 = 68.3 (°C)

Decimal	Binary	HEX
683	1010101011	2AB

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