22
Chapter 5
Specifications
All specifications are subject to change without notice.
Typical for 25 °C unless otherwise specified.
Specifications in italic text are guaranteed by design.
Analog input
Table 1. Generic analog input specifications
Parameter
Conditions
Specification
A/D converters
Four dual 24-bit, Sigma-Delta type
Number of channels
8 differential
Input isolation
500 VDC minimum between field wiring and USB
interface
Channel configuration
Software programmable to match sensor type
Differential input voltage
range for the various sensor
categories
Thermocouple
±0.080 V
RTD
0 V to 0.5 V
Thermistor
0 V to 2 V
Semiconductor sensor
0 V to 2.5 V
Absolute maximum input
voltage
±C0x through ±C7x relative to GND
(pins 9, 19, 28, 38)
±25 V power on, ±40 V power off
Input impedance
5 G
Ω
, min
Input leakage current
Open thermocouple detect disabled
30 nA max
Open thermocouple detect enabled
105 nA max
Normal mode rejection ratio
fIN = 60 Hz
90 dB min
Common mode rejection
Ratio
fIN=50 Hz/60 Hz
100 dB min
Resolution
24 bits
No missing codes
24 bits
Input coupling
DC
Warm-up time
30 minutes min
Open thermocouple detect
Automatically enabled when the channel pair is
configured for thermocouple sensor.
The maximum open detection time is 3 seconds.
CJC sensor accuracy
15 °C to 35 °C
±0.25 °C typ,±0.5 °C max
0 °C to 70 °C
–1.0 °C to +0.5 °C max
Channel configurations
Internally, the device has four, dual-channel, fully differential A/Ds providing a total of eight differential
channels. The analog input channels are therefore configured in four channel pairs with CH0/CH1 sensor
inputs, CH2/CH3 sensor inputs, CH4/CH5 sensor inputs, and CH6/CH7 sensor inputs paired together. This
channel-pairing
requires the analog input channel pairs be configured to monitor the same category of
temperature sensor. Mixing different sensor types of the same category (such as a type J thermocouple on
channel 0 and a type T thermocouple on channel 1) is valid.
Channel configuration information is stored in the EEPROM of the isolated microcontroller by the firmware
whenever any item is modified. Modification is performed by commands issued over USB from an external
application, and the configuration is made non-volatile through the use of the EEPROM.
