Arroyo Instruments TECPak 585 Series, User Manual

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Page 30 · TECPak User’s Manual
For example, if V was 1.00V, T
ANALOG-HIGH
was 200 and T
ANALOG-LOW
was -100, then
T
SETPOINT
would be 20°C:
T
SETPOINT
= (1.00 / 2.5 * (200 – (–100)) + (–100), or
T
SETPOINT
= (1.00 / 2.5 * (200 + 100)) – 100 = 20
To achieve less sensitivity per
°
C, you can narrow the high and low temperature
points to the actual operating range you need (perhaps T
ANALOG-LOW
of 10°C and
T
ANALOG-HIGH
of 40°C, for example). In addition, you can change the resolution of
the analog input from 1 ° C, 0.1 ° C, or 0.01 ° C, which is low the sensitivity to noise
on the input. Both of these changes can be done using Arroyo Control , or via
the TEC:ANALOG:THIGH, TEC:ANALOG:TLOW, or TEC:ANALOG:RES
commands.
Because the Analog Set Point input shares the measurement input with the
remote sensor input, when using RTD 4-wire measurement mode, the Analog
Set Point Input is disabled.
Analog Set Point Input in Current (ITE) Mode
For TECPaks running firmware version 1.38 or later, the analog set point input
allows the user to change the ITE set point using a voltage signal. The analog
input function must be enabled with the TEC:ANALOG:MODE command, and
the instrument set to ITE mode. When in this configuration, the ITE set point is
ignored, and the ITE current is controlled exclusively via the analog input.
The voltage input range goes from 0V to 2.5V, and the transfer function is:
ITE
SETPOINT
= ITE
LIMIT
* (V – 1.25)
Where V is the voltage input, in volts, and ITE
SETPOINT
is the resulting current set
point, in Amps. As can be seen from this equation, the full range of the analog
input corresponds to – ITE
LIMIT
to +ITE
LIMIT
, so the sensitivity of the input function
can be adjusted by raising or lowering the limit.
Because the Analog Set Point input shares the measurement input with the
remote sensor input, when using RTD 4-wire measurement mode, the Analog
Set Point Input is disabled.
Analog Monitor Output
The second analog signal is a monitor output that produces a voltage output
that tracks the actual voltage across the sensor. Because the bias current is
fixed, the actual sensor resistance can be easily calculated using Ohm’s Law,
and then using the Steinhart-Hart formulas, the actual temperature can then be
calculated.