Vaisala Drycap DMT152, User Manual

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4.3.3 Power Supply Requirements
The DMT152 transmitters are designed to operate with a supply voltage of 15 … 28 VDC
(voltage output version) or 21 … 28 VDC (current output version). When only the RS-485
output is used, 11 … 28 VDC is enough in typical measurement conditions.
When measuring in pressures 20 … 50 bar
a
(290 … 725 psi
a
) or in temperatures −40 … 0 °C
(−40 … 32 °F), a supply voltage of 21 … 28 VDC is required.
The power supply should maintain the voltage for all load conditions. Voltage fluctuations
must be smaller than 0.3 V, as continuous supply voltage fluctuation may interfere with the
auto-calibration function.
• If auto-calibration has failed due to voltage fluctuation, you can verify it using the STAT
command on the serial line. See Show Transmitter Status (page 33) .
• If auto-calibration fails repeatedly, the Autocal error code will be activated. See Error
Codes (page 58) .
Current consumption during normal operation is 20 mA. Consumption increases during auto-
calibration and sensor purge. The maximum current consumption is 220 mA pulsed current.
DMT152 can be powered by the MI70 indicator or the Vaisala USB cable. However,
the power supplied by these devices may not be enough for all functions of the
transmitter (for example, the current output).
If you are using a separate power supply in connector I, connect the power supply
first before connecting the USB cable or the MI70 indicator. The order is
important, since the transmitter will use the power supply that is connected first.
4.4 Loop-Powered Display
DMT152 can be connected to a loop-powered external LED display. The display provides a
reading of the output parameter. The display is powered by the 4 ... 20 mA current signal, so
there is no need for an external power supply.
Two models are available:
• Nokeval 301 (Vaisala order code 226476)
• Nokeval 302 (with alarm relays, Vaisala order code 234759)
The display is delivered at its default settings. Configure the display functions and scaling
according to the documentation delivered with the display. For a wiring example, see Figure 7
(page 20) .
The loop resistance of the display must be included in the loop resistance
calculation for the complete current loop. For the loop resistance of the display,
refer to the manufacturer’s documentation.
Chapter 4 – Installation
19