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Introduction
7
• Measured heater current differs from desired value: The CTC100’s output is nonzero, and the current flowing out of the positive terminal differs from the desired current by
more than 0.25A. This error can occur if the CTC100 is out of calibration. It can also mean
that the CTC100 has been damaged and is no longer capable of correctly regulating its
output current or of producing its rated output current.
• Current at + and – heater terminals is different: The CTC100’s output is non-zero,
and the current flowing out of the card’s positive terminal is not the same as the current
flowing into the negative terminal. This error can occur if one of the leads is shorted to an
external ground.
• Output is off but heater current was detected: The CTC100’s output is set to zero,
but current is flowing into the negative terminal. This error may indicate that the heater is
shorted to a power source other than the CTC100. It can also indicate a failure of the
CTC100’s output circuit.
• Output card overheated: Either the resistance of the heater is less than 10 ohms; the
positive and negative terminals are shorted to each other; the ambient temperature is too
high; or the CTC100’s chassis fan is not working. Try reducing the maximum output voltage
or current, and make sure the front panel fan is running.
±10V analog I/O channels
Each of the four analog I/O channels has a BNC connector on the back panel of the CTC100.
The outer shell of the connector is grounded.
Each analog I/O channel can be an input (±10V, 24-bit ADC) or an output (±10V, 16-bit
DAC).
Although they aren’t as accurate as the dedicated sensor inputs and heater outputs, the analog
I/O channels can be used to read temperature sensors and drive heaters. If used to drive a heater,
each analog I/O channel can only supply up to 30 mA of current. Furthermore, because of their
limited accuracy, when set to 0 V the analog outputs may still feed a small amount of power to the
heater. This residual current can be eliminated by placing a diode in series with the heater and
increasing the channel’s Lo Lmt setting to about 0.5V (to prevent integral windup).
Relays, digital I/O, and virtual channels
The CTC100 has four relays, each rated for up to 5A of current. The connector for the relays is a
single 12-pin pluggable terminal block. The four relays are labeled “A” through “D”, and each relay
has three connections labeled “NC” (normally closed), “COM” (common), and “NO” (normally
open). The relay is in its “normal” or “deactivated” state when the CTC is turned off, when its
outputs are not enabled, or when the relay is set to 0. In this state, the “NC” pin is connected to the
“COM” pin and the “NO” pin is unconnected. When the relay is set to 1 and the outputs are
enabled, the relay is activated: the “NO” pin is connected to the “COM” pin and the “NC” pin is
unconnected.
The relays appear on the CTC100 display as a single 4-bit integer value between 0 and 15. If no
relays are activated, the value is 0. Each relay, if activated, adds the following to the displayed
value:
Relay
A
B
C
D
Value
1
2
4
8
CTC100 Programmable Temperature Controller