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The following information is provided for customers interested in calibrating the TRH-160 Probe with their own humidity calibration equipment. Under typical use in controlled residential and commercial indoor environments, the TRH-160 Probe should not require re-calibration for 5+ years.
The TRH-160 Probe requires 5 vdc excitation at 2 ma max.
Warm-up time (the time from when 5 vdc power is applied until the humidity output signal is stable) is 100 milliseconds (0.1 second).
The probe has four 24 awg insulated leads with the following colors and functions:
| Black | Signal return (ground) |
| White | 5 vdc excitation |
| Green | Humidity output signal |
| Red (or Yellow) | 30k ohm Thermistor |
CAUTION! The TRH-160 Probe does not have a reverse blocking diode. The Pace XR5 Data Logger pulses current-limited power to the TRH-160 which prevents damage if the probe is incorrectly wired.
If connecting the TRH-160 to a device other than the XR5 Data Logger, reversing the power and ground leads will destroy the probe, so carefully check your connections before applying power!
The Humidity output signal is approximately 0.45 vdc at 0% RH and 1.95 vdc at 100% RH. Each TRH-160 probe ships with individual scaling values typed on a label bonded to the probe's cable. The first scaling value is the Offset (a negative value), the second number is the Slope.
Re-Calibration (to be performed only if required, typically after a long interval (years) of use)
In order to perform a re-calibration of the TRH-160, the probe must be placed in an environment (humidity chamber) with a precisely known humidity and stable temperature close to 25°C. Read and note the output voltage of the TRH-160 at a precise, stabilized, low RH environment, and at a precise, stabilized, high RH environment. (For example, read the TRH-160's output voltage at 20% RH and 70% RH). Then, using these two Voltage vs % RH readings, apply the following formulas:
Y2 = High % RH value
X2 = voltage output at High % RH
Y1 = Low % RH value
X1 = voltage output at Low % RH
Slope m = (Y2 - Y1) / (X2 - X1)
Offset b = Y1 - (m)X1
Example:
At 20% RH, TRH-160 output voltage reads 0.75v
At 70% RH, TRH-160 output voltage reads 1.50v
Slope m = (70 - 20)/(1.50 - 0.75) = 66.67
Offset b = 20 - (66.67 * 0.75) = -30.0
Note: for customers using an XR5 with the TRH-160, the TRH-160 output voltage can be read by sending a Setup to the XR5 with the RH channel's Type set to "0 - 2.5V", the Slope set to 1 and the Offset to 0. And set Sensor Excitation in the Main tab to "150 ms". This will cause the XR5 to read the TRH-160's humidity signal in volts.
Tel: (704) 799-0688 Fax: (704) 799-0177 Email: sales@pace-sci.com
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