Linear Technology LTC2983 - Page 61

LTC2983
61
2983fc
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CUSTOM THERMOCOUPLES
In order to simplify the temperature field, temperature
values are input in Kelvin as an unsigned value, but the
final temperatures reported by the LTC2983 are reported
in °C or °F. The sensor temperature (Kelvin), follows the
convention shown in Table 70, where the first 14 bits
are the integer part and the remaining 10 bits are the
fractional part.
In this example, a custom thermocouple tied to CH1, with
a cold junction sensor on CH2, is programmed with the
channel assignment data shown in Table 71 (refer to Figure
6 for similar format). In this case the custom data begins at
memory location 0x250 (starting address is 0). The start-
ing address (offset from 0x250) is entered in the custom
thermocouple data pointer field of the channel assignment
data. The table data length –1 (9 in this example) is entered
into the custom thermocouple data length field of the
thermocouple channel assignment word. Refer to Table 68
where the number of six byte entries is 10.
Table 70. Example Thermocouple Temperature Values
BYTE 3 BYTE 4 BYTE 5
B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Temperature 2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
2
–1
2
–2
2
–3
2
–4
2
–5
2
–6
2
–7
2
–8
2
–9
2
–10
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
99.1 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 0 0
1 1 0
135.4 0 0 0 0 0 0 1 0 0 0 0 1 1 1 0 1 1 0 0 1 1 0 0 1
273.15 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 0 1 1 0 0 1
361.2 0 0 0 0 0 1 0 1 1 0 1 0 0 1 0 0 1 1 0 0 1 1 0 0
522.1 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 1 1 0 0 1 1 0
720.3 0 0 0 0 1 0 1 1 0 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1
811.2 0 0 0 0 1
1 0 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0
922.5 0 0 0 0 1 1 1 0 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0
1000 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
Table 71. Custom Thermocouple Channel Assignment Data
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY
DATA
MEMORY
ADDRESS 200
MEMORY
ADDRESS 201
MEMORY
ADDRESS 202
MEMORY
ADDRESS 203
(1) Thermocouple
Type
Type Custom 5 01001 0 1 0 0 1
(2) Cold Junction
Channel Pointer
CH
2
5 00010 0 0 0 1 0
(3) Sensor
Configuration
Single-Ended,
10µA Open Circuit
4 1100 1 1 0 0
Not Used Set These Bits to 0 6 000000 0 0 0 0 0 0
(4) Custom
Thermocouple Data
Pointer
Start Address = 0
(Start at 0x250)
6 000000 0 0 0 0 0 0
Custom
Thermocouple Data
Length-1
Data Length –1
= 9
(10 Paired Entries)
6 001010 0 0 1 0 0 1