Armstrong International
221 Armstrong Blvd, Three Rivers, MI 49093 - U.S.A.
Tel: (269) 279-3602 Fax: (269) 279-3130
Designs, materials, weights, and performance ratings are
approximate and are subject to change without notice.
Visit armstronginternational.com for the most updated information.
Page 15 of 36
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4.0 - Current Loop I/O
The Emech
®
current loop hardware is capable of operating across the standard 4-20mA range. By default the linear control range, for both
input and output, has been limited to the range of 5-19mA.
Values outside this range on the loop input represent non-linear behaviors such as closed, cold only or hot only.
Values outside the 5-19mA range on the loop output are used to signal error conditions. Contact Armstrong for customized configuration
settings.
WARNING!
The voltage range required for the latest version actuators current loop input will vary from 3.5VDC for
4mA of current to 5.6VDC for 20mA of current at the terminals. Therefore, the PLC controller will need
to be setup to provide at the actuator 3.5VDC at 4mA to a maximum of 5.6Vdc at 20mA.
If the voltage at the actuator current loop input terminals exceed about 9VDC or about 50mA threshold,
the input circuit protection will be activated and the current loop signal will be clamped to ground.
This has the effect of ‘locking out the PLC signal and closing the actuator on “loss of signal”. This
situation remains until the PLC signal is reduced below this threshold, whereby control is restored.
Therefore, the PLC controller must be setup to avoid sending a current loop signal to the actuator of
50mA or higher.
4.1 - Standard Configuration of Current Loop Input for Temperature Mode
The unit will respond to the current loop input when in REMOTE mode only (Refer to Section 5.4). The full control range in Temperature
mode is 0-100°C or 32-212°F. This corresponds to a Loop Input range of 5 to 19mA. Calibrate the current loop transmitter (usually an
external PLC or Controller) according to the following equations.
Temperature Linear Range Calculation in Degrees Celsius (°C)
Current input (mA) = (0.14 x Temperature required (°C)) + 5
Temperature Linear Range Calculation in Degrees Fahrenheit (°F)
Current input (mA) = (0.0778 x Temperature required (°F)) + 2.511
If given a signal outside the 5-19 mA range, the Actuator will not control temperature, but will move to a fixed angle depending on the
Actuator configuration. Refer to Figure 4.1 for a graphical description of Loop Input behavior in Temperature Controller mode for several
standard configuration types.
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