General Information The Pyromation Series 401 RTD temperature transmitter is a “two wire” loop powered resistance to current transducer. This transmitter will produce a linearized (4 to 20) mA dc output current proportional to the temperature of the RTD temperature sensor. The transmitter’s small size allows universal mounting inside Series 300, 400, and 900 screw cover heads, Series 800 explosion-proof, thermostat housings, and panel surface mounting using two 6-32 screws1 . The transmitter is designed for an operating ambient temperature of (-30 to 65) °C [(-22 to 149) °F]. Power Supply The transmitter is designed for a nominal 24 V dc power supply. The transmitter will operate over a range of (9 to 36) V dc depending on the resistive load. Use the following formulas to determine the maximum resistive loading (RL) allowed for the power used, or to determine minimum supply voltage (V) required for fixed resistive loads. The formulas assume a maximum current of 20 mA. VMIN = 20 mA × RLOAD + 9 V dc RMAXLOAD = (VSUPPLY – 9 V dc ) / 20 mA One power supply can be used for several transmitter loops. Each loop must have only one transmitter in it and all loops must be wired in parallel. Do not forget to observe the maximum current rating for your power supply. Note: If used in a manner not specified by the manufacture, the protection provided by the equipment may be impaired. Wiring The terminal block on the transmitter can accept wire from 14 to 24 gauge. Shielded or conduit encased (twisted pair) cable is required from the transmitter to the controller, including the sensing element and lead wire. Note that low voltage lines should be run in separate conduit isolated from high voltage or high current carrying lines. Open Sensor Indication When an RTD has failed due to an open sensor, the transmitter will indicate an error. The way the error is produced is by either driving the current low, under 4 mA (downscale burnout) or by driving the current high, above 20 mA (upscale burnout). Upscale burnout is standard for all Pyromation transmitters. However, the burnout indication does not apply to a break in the lead compensation loop. In this case, the burnout signal will drive the transmitter either high or low depending upon which lead has broken. RTD ELEMENT POWER SUPPLY