TC-32 User's Guide
Functional Details
13
Data linearization
After the CJC correction is performed on the measurement data, an on-board microcontroller automatically
linearizes the thermocouple measurement data using National Institute of Standards and Technology (NIST)
linearization coefficients for the selected thermocouple type.
The measurement data is then output as a 32-bit floating point value in the configured format (voltage or
temperature).
Open-thermocouple detection (OTD)
The TC-32 is equipped with OTD for all analog input channel. With OTD, any open-circuit condition at the TC
sensor is detected by the software. An open channel is detected by the use of a pull up and pull down resistors
on the thermocouple inputs. An open thermocouple condition forces the input differential voltage outside of the
valid thermocouple voltage range. The software recognizes this as an invalid reading and flags the appropriate
channel. The software continues to sample all channels when OTD is detected.
Input leakage current
With OTD enabled, 75 nA (max) of input leakage current is injected into the TC. This current can cause an
error voltage to develop across the lead resistance of the TC that is indistinguishable from the thermocouple
voltage you are measuring. You can estimate this error voltage with the following formula:
error voltage = resistance of the thermocouple × 75 nA
To reduce the error, reduce the length of the TC to lower its resistance, or lower the AWG of the wire by using
a wire with a larger diameter. With open-thermocouple detection disabled, 2 nA (max) of input leakage current
is injected into the TC.
Digital I/O
The TC-32 provides up to eight digital inputs and 32 digital outputs that are electrically isolated from the host
computer and from the TC-32 analog circuits.
All DIO bits have internal pull-up resistors to 5 V that can be disconnected with the rear panel slide switches.
The recommended maximum length of the 50-pin cable used to connect the
DIGITAL I/O
connector to the
digital I/O signal source is 1 foot.
Digital inputs
The TC-32 provides \ digital inputs with rates of 500 port reads or single bit reads per second.
Digital input voltage ranges of 0 V to 15 V are permitted, with thresholds of 0.6 V (low) and 2.2 V (high).
Each digital input has a 100
kΩ pull-up resistor. Use the eight
PULL-UP ENABLE – DIN
slide switches to
enable or disable the 5 V pull-up option.
Digital outputs/temperature alarms
Each digital output is
open-drain
, which can of sink up to 100 mA for direct drive applications.
Each digital input has a 100
kΩ pull-up resistor. Use the eight
PULL-UP ENABLE – DOUT
slide switches to
enable or disable the 5 V pull-up option.
Optionally, you can configure each digital output as an alarm for each TC input. When an alarm is enabled, its
associated output line is driven to the appropriate state determined by the alarm options and input temperature.
You can also use the alarm outputs to control a device or application that indicates when a temperature
threshold has been exceeded.
The alarm configurations are stored in non-volatile memory and loaded at power up.
Alarm settings are applied when changed and at power on. Temperatures are constantly converted on enabled
channels and processed for alarm conditions regardless of the communications connectivity.
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