User manual for flow meter with pulse input SPI-94
8.
CURRENT OUTPUT VALUE CALCULATION
Let the current output parameters be:
“modE”
=
“on”
,
“OUt LO”
= 100,
“OUt HI”
= 200,
“Lo r”
= 5.0,
“Hi r”
= 5.0
Parameters
“Lo r”
and
“Hi r”
define working range of current output to 3,8 ÷ 21 mA.
Output current will be calculated for three displayed values „D”:
a) D = „17.5”
According to formula from page 31:
I
out
= (17.5-10.0) / (20.0-10.0) × 16 mA + 4 mA = 0.75 ·16 + 4 = 16 mA
Calculated I
out
do not exceeds the output working range (3 - 21 mA).
b) D = „20.5”
According to formula from page 31:
I
out
= (20.5-10.0) / (20.0-10.0) × 16 mA + 4 mA = 1.05 ·16 + 4 = 20.08 mA
Calculated I
out
do not exceeds the output working range (3 - 21 mA).
c) D = „30.0”
According to formula from page 31:
I
out
= (30.0-10.0) / (20.0-10.0) × 16 mA + 4 mA = 2 ·16 + 4 = 36 mA.
Calculated I
out
exceeds the output working range (3 - 21 mA), so current output will generate
current equal to the upper border of range defined by parameter
“Lo r”
i
“Hi r”
(it means
21 mA).
9.
THE MODBUS PRO
TOCOL HANDLING
Transmission parameters: 1 start bit, 8 data bits, 1 or 2 stop bit (2 bits are send, 1 and 2 bits
are accepted when receive), no parity control
Baud rate:
selectable from: 1200 to 115200 bits/second
Transmission protocol:
MODBUS RTU compatible
The device parameters and display value are available via RS-485 interface, as HOLDING-
type registers (numeric values are given in U2 code) of Modbus RTU protocol. The registers
(or groups of the registers) can be read by 03h function, and wrote by 06h (single registers) or
10h (group of the registers) accordingly to Modbus RTU specification. Maximum group size for
03h and 10h functions can not exceeds 16 registers (for single frame).
The device interprets the broadcast messages, but then do not sends the answers.
9.1.
LIST OF REGISTERS
Some parameters are located on two registers (higher word in first register, and lower word in
next one). After writing of one of them device controls result of their 32-bit value, and if it is
necessary corrects value of second register automatically. If appropriate modification is
impossible, both registers stay unaffected and device responds with error code 03h
(see:
TRANSMISSION ERRORS DESCRIPTION
).
38
i
