Dwyer Instruments Digihelic DHC Series

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Modbus

Communications Protocol Overview

Modbus

Communications Protocol Functions

The DHC supports the following functions.

Modbus

Communications Protocol Registers

Input Registers

The String data type is read as a stream of ASCII characters with the rst character

sent in the MSB of the rst register and the second character sent in the LSB of the

rst register and so on. If the string is shorter than the allotted size, the remaining bytes

will be zero padded.

Holding Registers

Pressure/Velocity/Flow Units: The unit selected is independent of the display unit.

Alarm High/Low Limit Status: The alarm status can be reset to inactive by writing

inactive to the status register. This is allowed only if Manual Alarm Reset is Enabled

and the process value no longer satises the alarm condition. In all other cases a

Modbus

communications protocol error is returned.

INPUT REGISTERS

0001-0002

0003-0004

0005-0006

0007-0008

0009-0010

0011

0012

0013

0014-0015

8001-8016

8017-8020

8021-8028

8029-8032

Pressure

Velocity

Flow

Peak

Valley

Set Point 1 Status

Set Point 2 Status

External Input Status

Error Flags

Model Number

Serial Number

Firmware Version

Date Code

32bit oat

16bit integer

32bit integer

String(32)

String(8)

String(16)

String(8)

0=Inactive, 1=Active

See Table Below

“DHC-XXX-XXX”

“XXXXX”

“X.X.X”

“XXXXXX

INPUT REGISTERS

0001-0016

0017

0018

0019

0020

0021-0022

0023-0024

0025-0026

0027-0028

0029

0030

0031-0032

0033-0034

0035

0036-0037

0038-0039

0040

0041-0042

0043

0044-0045

0046

0047

0048

0049

0050

0051

0052

0053

0054

0055

0056

0057

0058

Device Name

Process Mode

Pressure Unit

Velocity Unit

Flow Unit

Velocity K-Factor

Flow Area

Process Output Low

Process Output High

Voltage Output Range

Set Point 1 Enable

Set Point 1 Trigger Value

Set Point 1 Reset Value

Set Point 2 Enable

Set Point 2 Trigger Value

Set Point 2 Reset Value

Enable Alarm High Limit

High Alarm Limit

Enable Alarm Low Limit

Low Alarm Limit

Manual Alarm Reset

Power Up Alarm Inhibit

Alarm Delay

Alarm High Limit Status

Alarm Low Limit Status

Relay 1 Source

Relay 1 Action

Relay 2 Source

Relay 2 Action

Enable External Input

External Input Type

External Input Activation

Delay

Damping Time

String(32)

16bit integer

32bit oat

16bit integer

32bit oat

16bit integer

32bit oat

16bit integer

32bit oat

16bit integer

32bit oat

16bit integer

“DHC”

0=Pressure, 1=Velocity,

2=Flow

0=inWC, 1=ftWC, 2=mmWC,

3=cmWC, 4=PSI, 5=inHG,

6=mmHg, 7=mBar, 8=Pa,

9=kPa, 10=hPa, 11=ozin

0=ft/min, 1=m/s

0=ft

/min, 1=m

/hr

0.001-9.999

0.125-25ft

(0.0116-2.3226m

)

0=0-10V, 1=0-5V, 2=1-5V,

3=2-10V

0=False, 1=True

0=Disabled, 1=Enabled

0-3600

0=Inactive, 1=active

0=Off, 1=Set Point 1, 2=Set

Point 2,

3=Any Alarm,

4=High Alarm Limit, 5=Low

Alarm Limit, 6=External Input

0=Direct, 1=Reverse

0=Off, 1=Set Point 1, 2=Set

Point 2,

3=Any Alarm,

4=High Alarm Limit, 5=Low

Alarm Limit, 6=External Input

0=Direct, 1=Reverse

0=False, 1=True

0=Normally Open,

1=Normally Closed

0-3600

0-30

Display Errors

Error Flags

Bit Position Description

EADR

ouEr

Undr

ER 1

ER 2

ER 3

ER 4

ER 5

ER 6

ER 7

Invalid Address

Over Range

Under Range

Sensor Range Exceeded

Sensor Error

No Sensor

User Settings Invalid

Factory Settings Invalid

External Memory Failure

Internal Memory Failure

Modbus

communications protocol installations should comply with

Modbus

Communication Protocol over Serial Line Specication

and Implementation Guide V1.02, Modbus

Organization, Inc., 2006

NOTICE

Communications wiring must be in a daisy-chain fashion. Star

connections and T connections are not permitted

NOTICE

Dwyer Instruments Digihelic DHC Series - Page 16

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