AMETEK 7250 Digital Stick - Manual (Page 3)

3
There are currently two
different software protocol
versions available (7252
and 7255). In actuality, the
‘protocols’ are very similar.
The significant difference
is the amount of product
measurements transmitted
within the data string. A unique
start character is also sent at
the beginning of each data
string to identify the data string
type, or hence, the ‘protocol’.
Communication Parameters
(fixed)
baud 9600
parity odd
data bits 7
start bits 1
stop bits 1
Data Format
The data string is in ASCII format and the total
data string transmission time is roughly one (1)
second for the 7255 and three (3) seconds for the
7252.
Approximately 100ms after power up, a start
character (“=” for 7252, “<” for 7255) is transmitted
and the first product position is measured and
transmitted. Subsequent position measurements
and transmissions continue every 100ms until
the complete number of products has been
transmitted. One interface position is transmitted
immediately following the final product position.
All temperature data is then transmitted along
with a final 2-digit ASCII Checksum followed by
a Carriage Return character to end the string.
Note that a comma character (‘,’) is transmitted
between each position and temperature
measurement (see example below).
The probe will continue to take level and
temperature readings and the data string
transmission process continues repeatedly as
long as power is applied to the probe.
The data string length is protocol dependent (i.e.
269 bytes for 7252; 134 bytes for 7255). The data
string is comprised of a start character, product
levels (protocol dependent: 25 for 7252; 10 for
7255), 1 interface level, and 5 temperature sensor
levels followed by a 2-digit ASCII Checksum and a
carriage return character ().
For probes ordered with only 1 temperature
sensor (i.e. T1 or R1), the temperature reading
value of that one sensor is placed in all five
temperature data locations in the string.
NOTE: Data values outside the ranges specified
above indicate an error condition.
Data String
s,ppp.pppp,ppp.pppp,…
...,ppp.pppp,iii.iiii,+/-tt.t,…,+/-tt.t,CC
s: Start Character
(identifies protocol, type and quantity of
following data)
ppp.pppp: Product
(000.0000” to 600.0000”)
iii.iiii: Interface
(000.0000” to 600.0000”)
(Note: Interface = 000.0000 if Stik is
ordered with only 1 float)
+/-tt.t: Temperature
(-40.0ºC to +85.0ºC)
CC: 2 digit ASCII checksum
(see calculation process below)
: End of data string - carriage return
A value of “999.9999” will be transmitted if there is
an error in the product or interface levels.
A value of “-99.9” will be transmitted if there is an
error in the temperature sensor level.
Fig. 1 Power Consumption